Boston cream filling, also known as Boston cream pie filling, is a classic custard cream used in the famous Boston cream pie. It consists of a vanilla custard or pastry cream that is thickened with eggs and cornstarch, and often flavored with chocolate. Boston cream filling has a rich, creamy and smooth texture that pairs perfectly with cake or dough layers in desserts. Let’s take a deeper look into the ingredients that go into making this iconic cream filling!
The Main Ingredients
There are five main ingredients that make up traditional Boston cream filling:
- Milk – Whole milk or cream provides the creamy richness and fat content.
- Sugar – Granulated white sugar sweetens the custard.
- Egg yolks – Egg yolks thicken the custard when heated.
- Cornstarch – Cornstarch aids the egg yolks in thickening the mixture.
- Vanilla extract – Pure vanilla extract provides classic flavor.
By combining these simple ingredients and cooking them together on the stovetop, you get a luscious vanilla pastry cream that perfectly fills and complements cakes and pastries.
The Purpose of Each Ingredient
Let’s explore the purpose and role that each of the main ingredients plays in making Boston cream filling:
Milk
Whole milk or heavy cream provides the body, richness and fat that gives Boston cream its ultra-smooth, creamy texture. Non-fat or low-fat milk can be used, but will result in a less rich consistency. The milk proteins and butterfat content aid in creating a custard with the proper density.
Sugar
Granulated white sugar, either baker’s or common table variety, adds sweetness to balance the creamy vanilla notes. The right amount of sugar prevents the custard from tasting too eggy. Superfine sugar can be used as well, but dissolves more quickly and may cause burning, so it requires extra care when cooking.
Egg Yolks
Egg yolks are key for thickening and binding the pastry cream. As the yolks cook, the proteins denature and thicken the custard. Yolks add a rich taste and yellow color. Using whole eggs can make the filling too eggy.
Cornstarch
A touch of cornstarch complements the egg yolks and ensures the filling sets up properly and remains nicely thickened. It prevents the custard from becoming too thin or runny. Cornstarch thickens at a higher temperature than eggs alone.
Vanilla Extract
Vanilla extract infuses the custard with the quintessential flavor associated with Boston cream pie and vanilla custards. Use real vanilla only, not imitation vanilla which has a less robust flavor. Vanilla beans can also be steeped in the milk for more intense vanilla taste.
Standard Proportions
While variations exist, standard proportions for traditional Boston cream filling are:
- 1/4 cup cornstarch
- 2 cups whole milk
- 1 cup heavy cream
- 1/2 cup granulated white sugar
- 5 egg yolks
- 2 teaspoons vanilla extract
This makes enough silky-smooth pastry cream to fill one 9-inch single layer cake or several cream puffs. The ingredients can be doubled or tripled for more filling or layered cakes.
Complete Ingredient List
In addition to the core ingredients, Boston cream filling often includes extras for even more flavor and richness. Here is a complete list of what you might find in a Boston cream filling recipe:
- Milk – whole milk or heavy cream
- Sugar – granulated white, fine granulated or superfine
- Egg yolks
- Cornstarch
- Butter – for extra richness
- Vanilla extract
- Salt – a pinch enhances flavors
- Chocolate – melted and cooled for chocolate cream
- Rum or brandy (optional) – boosts vanilla notes
- Lemon zest (optional) – brightens flavor
As you can see, while the base of milk, sugar, eggs, cornstarch and vanilla is constant, there is room for additions and tweaks to create your own signature Boston cream filling.
The Different Methods to Make Boston Cream Filling
Boston cream filling is made by cooking a custard on the stovetop or baking it in the oven. Here are the main preparation methods:
On the Stovetop
The traditional way is cooking the custard right on the stovetop in a saucepan. The ingredients are whisked together and heated while stirring constantly until thickened. This requires close monitoring so the eggs don’t overcook and curdle. Using a double boiler setup can help prevent this.
In the Oven
A hands-off method is baking the custard in a hot water bath in the oven, known as a bain-marie. The bowl with custard sits in a larger pan filled with hot water, gently heating and thickening the cream. Just keep an eye on it so it doesn’t overbake.
With Instant Pudding
For speed and ease, Boston cream filling can be made by whisking instant vanilla pudding mix into cold milk and cream, then letting it thicken in the fridge. This gives you a creamy base in minutes without cooking.
With Pastry Cream Mix
Specialty pastry cream mixes can be prepared by cooking with milk and/or butter on the stovetop or in the oven. These provide a convenient shortcut if you don’t want to make the custard completely from scratch.
With Custard Powder
If you can find it, custard powder is a handy ingredient for quick and easy pastry cream. Simply mix the powder with milk and/or cream and cook briefly until thickened.
Tips for Making the Perfect Boston Cream Filling
Follow these handy tips when making your Boston cream pie filling for best results every time:
- Use very fresh eggs for safest results.
- Make sure to cook sufficiently to activate the cornstarch and egg thickening power.
- Strain the finished custard through a fine mesh sieve for silky smooth texture.
- Press plastic wrap directly onto the surface to prevent a skin forming.
- Chill filling fully before using for easiest spreading and slicing.
- Store leftover filling in the refrigerator up to 4 days.
Variations
While traditional Boston cream filling is vanilla, the basic custard can be turned into creative flavor interpretations. Get inspired by these delicious variations:
Chocolate Boston Cream
Swirl melted dark, milk or white chocolate into the finished vanilla cream. The chocolate sits in thick veins throughout.
Coconut Boston Cream
Add coconut extract and shredded coconut to the filling for tropical flavor.
Coffee Boston Cream
Dissolve espresso powder or instant coffee into the warm cream and increase sugar slightly to make mocha cream.
Spiced Boston Cream
Infuse the milk with cinnamon, cardamom, cloves, nutmeg or other baking spices.
Fruit Boston Creams
Fold fruit preserves, jam or sauce into the finished cream for bright fruit flavors. Try strawberry, raspberry, lemon or passionfruit.
Boozy Boston Cream
For adults, spike the filling with rum, brandy, Kahlua, amaretto or other liqueurs.
The possibilities are endless for reinventing classic Boston cream into inspired new flavor combinations!
Storing Boston Cream Filling
Properly stored Boston cream filling keeps well for 4-5 days in the refrigerator, and it can be frozen for longer term storage:
Refrigeration
- Keep filling in an airtight container in the fridge.
- Press plastic wrap directly on the surface before sealing to prevent skin forming.
- Use within 4-5 days for best quality.
Freezing
- Portion filling into freezer bags or airtight containers, leaving headspace.
- Remove as much air as possible before sealing.
- Freeze for 2-3 months.
- Thaw overnight in fridge before using.
How to Use Boston Cream Filling
This versatile custard cream is delicious sandwiched between cake layers, stuffed into doughnuts and pastries, or eaten straight off the spoon! Here are top ways to enjoy Boston cream filling:
Boston Cream Pie
Fill and frost layers of yellow sponge cake or butter cake with the cream for the iconic Boston cream pie dessert.
Doughnuts
Pipe or inject the filling into baked, fried or glazed doughnuts for Boston cream-filled treats.
Eclairs and Cream Puffs
Fill profiteroles, eclairs, cream puffs and other choux pastries with the creamy custard.
Tarts
Spread into pre-baked tart shells, top with fruit if desired.
Creamy Dessert Sauces
Thin with milk or cream to use as a rich sauce over cakes, brownies, ice cream and fresh fruit.
Pancakes and Crepes
Layer inside sweet crepes or pancakes and top with chocolate sauce.
Milkshakes
Blend into thick milkshakes for a decadent dessert drink.
Troubleshooting Boston Cream Filling
Here are some common issues when making Boston cream filling and how to avoid them:
Filling is Too Thin
The cornstarch or eggs were undercooked. Be sure to cook completely until very thick. Chill for at least 2 hours to thicken further before using.
Filling is Lumpy
If lumps form, strain through a fine mesh sieve after cooking to remove them for smooth texture.
Filling Curdled
Curdling occurs if eggs overcook or mixture is heated too quickly. Use low heat and stir constantly next time.
Filling Weeps Liquid
This separation happens if filling was moved too soon after cooking. Let it cool undisturbed for 30 minutes first.
Skin Forms on Filling
To prevent a skin forming on the filling surface, press plastic wrap directly onto the cream before refrigerating.
Boston Cream Filling FAQs
Here are answers to some frequently asked questions about Boston cream pie filling:
What is Boston cream made of?
Boston cream is made by thickening milk, cream, eggs, sugar and cornstarch into a vanilla-flavored custard pastry cream.
Is Boston cream filling the same as custard?
Yes, it is essentially a type of vanilla custard. The two terms refer to the same thick, creamy egg-based filling.
Is Boston cream filling cooked?
Typically, yes – Boston cream filling is cooked either on the stovetop or baked in the oven to thicken the eggs and cornstarch.
Can you make Boston cream from a mix?
Yes, instant pudding mixes or prepared pastry cream mixes can shortcuts to making Boston cream without cooking a custard completely from scratch.
Do you refrigerate Boston cream filling?
Yes, always refrigerate the filling after making and again after assembling the dessert to prevent spoilage and so it sets up firmly.
Conclusion
With its luscious vanilla custard flavor and smooth, creamy texture, it’s easy to see why Boston cream filling is so beloved. This rich staple can elevate everything from cakes to doughnuts with its signature taste and decadence. Whether you opt for the classic stovestop method or convenient shortcut, perfecting this versatile cream is a baking skill that enables endless dessert possibilities. The next time a recipe calls for silky pastry cream or vanilla custard, reach for homemade Boston cream filling and enjoy its delightful results.
