High Protein Boston Cream Cake (Protein Custard Filling)

You want classic bakery energy… but with better macros.

This High Protein Boston Cream Cake gives you soft vanilla cake, creamy protein custard filling, and a glossy chocolate ganache top — all layered into one nostalgic, impressive dessert.

It looks like effort.
It tastes like childhood.
It secretly supports your protein goals.

Let’s build it.

Why This Recipe is Awesome

The original Boston cream pie (which is actually a cake, not a pie) is famous for:

• Fluffy vanilla sponge
• Thick pastry cream center
• Chocolate glaze on top

We’re keeping that structure — but upgrading it with:

• Protein-enriched vanilla cake
• High-protein custard filling
• Balanced sweetness
• Real structure without being dense

It’s indulgent, but smarter.

Ingredients You’ll Need

For the Protein Vanilla Cake

• 1 cup oat flour
• ¼ cup vanilla protein powder
• 1 teaspoon baking powder
• 2 eggs
• ½ cup Greek yogurt
• ¼ cup maple syrup or honey
• ¼ cup milk
• 1 teaspoon vanilla extract
• Pinch of salt

For the Protein Custard Filling

• 1 cup milk
• ½ cup Greek yogurt
• ¼ cup vanilla protein powder
• 2 tablespoons maple syrup
• 1 tablespoon cornstarch
• 1 teaspoon vanilla extract

For the Chocolate Ganache

• ¾ cup dark chocolate chips
• 2–3 tablespoons milk or coconut milk

Step-by-Step Instructions

1. Bake the Cake

Preheat oven to 350°F (175°C).

Grease and line an 8-inch round cake pan.

In a bowl, combine oat flour, protein powder, baking powder, and salt.

In another bowl, whisk eggs, Greek yogurt, maple syrup, milk, and vanilla.

Combine wet and dry ingredients gently until smooth.

Pour into pan and bake 22–28 minutes until set and lightly golden.

Cool completely before slicing.

2. Make the Protein Custard

In a saucepan over medium heat, whisk milk, cornstarch, and maple syrup until slightly thickened (about 3–5 minutes).

Remove from heat and whisk in Greek yogurt, protein powder, and vanilla.

Whisk until smooth and creamy.

Let cool — it will thicken more as it chills.

For ultra-smooth texture, strain or blend briefly.

3. Slice and Fill

Once cake is fully cooled, slice horizontally into two even layers.

Spread the protein custard evenly over the bottom layer.

Place the top layer gently over the filling.

Chill 20–30 minutes to help set before adding ganache.

4. Make the Ganache

Microwave chocolate chips with milk in 20-second intervals, stirring each time until smooth.

Let cool slightly so it thickens but remains pourable.

Pour over the top of the cake and gently spread to edges, letting some drip slightly down the sides if you’re feeling dramatic.

Chill until ganache sets.

Texture Expectations

This isn’t a dense protein brick.

You should get:

• Soft, tender cake
• Creamy, smooth custard center
• Silky chocolate top
• Balanced sweetness

If it feels dry, it was likely overbaked.

Common Mistakes to Avoid

1. Overbaking the cake
Protein-based batters dry out quickly.

2. Adding protein powder to boiling milk
Let it cool slightly first to avoid clumping.

3. Filling while cake is warm
It will melt the custard.

4. Making ganache too thin
Let it cool slightly before pouring.

5. Using too much protein powder
Texture > extra grams.

Alternatives & Variations

• Chocolate cake version: Replace 2 tablespoons flour with cocoa powder.
• Mocha twist: Add ½ teaspoon espresso powder to ganache.
• Lower sugar: Use sugar-free chocolate chips.
• Dairy-free: Use plant milk and dairy-free yogurt.
• Higher protein boost: Add 1 tablespoon extra protein powder to custard + 1 tablespoon milk to balance.

Approximate Protein Boost

Compared to traditional Boston cream cake, this version significantly increases protein thanks to:

• Greek yogurt
• Protein powder
• Eggs

Still dessert. Just upgraded.

FAQ

1. Does it taste like traditional Boston cream cake?

Very close — slightly less sweet, slightly more balanced.

2. Can I make it ahead of time?

Yes! It’s even better the next day once fully chilled.

3. Can I freeze it?

Yes, though the custard texture may soften slightly after thawing.

4. Why is my custard too thin?

It likely needs more chill time — or slightly more cornstarch next time.

5. What protein powder works best?

Vanilla whey blends give the smoothest custard texture.

6. Can I turn this into cupcakes?

Absolutely — bake in muffin tins and pipe custard into centers.

7. Is it truly high protein?

Compared to the classic version — yes. It’s a meaningful upgrade while still tasting indulgent.

Final Thoughts

This High Protein Boston Cream Cake delivers full bakery nostalgia — without ignoring your goals.

Soft cake.
Creamy protein custard.
Glossy chocolate top.

It looks impressive.
It slices beautifully.
It tastes like you didn’t compromise.

Classic dessert energy. Modern macro mindset.

What are we upgrading next?