Banana Cake Filling Recipe

This banana cake filling is a cooked banana custard made with 2 ripe bananas, whole milk, egg yolks, sugar, and cornstarch, finished with butter and vanilla. It takes about 20 minutes of work plus 2 hours in the fridge, and it fills one 2 layer 8 inch cake generously.

The mashed banana cooks right into the custard instead of being folded in at the end. That gives the whole filling a real banana flavor, and the cornstarch and yolks set it thick enough to stay put between layers. It lands somewhere between banana pudding and pastry cream, with an optional pinch of cinnamon or nutmeg.

What One Batch of Banana Filling Covers

• Yield: about 2 cups, a thick layer for one 2 layer 8 inch cake
• Time: 10 minutes prep, 6 to 8 minutes on the stove, at least 2 hours to chill
• Thickener: 2 tablespoons cornstarch and 2 egg yolks for 1 cup milk and 2 large bananas
• Keeps: up to 3 days in the fridge, not suited to freezing
• For a 9 inch cake or three layers: make 1½ batches

Picking Bananas for a Cooked Banana Filling

Use large bananas with yellow peels speckled in brown that still feel a little firm. Those have full banana flavor but still mash into a thick purée. Green bananas taste starchy and leave hard lumps. Very dark, mushy ones taste fermented and make the filling loose, so save those for banana bread.

Mash them until mostly smooth. A few small bits are fine and give the filling some texture. Stir the lemon juice in right away, since it slows browning and adds a little tang that keeps the filling from tasting flat.

Whole milk gives the creamiest body. Oat milk works too, though the texture comes out slightly grainy.

Cooking the Banana Custard on the Stove

Whisk the sugar, cornstarch, and salt together in a medium saucepan before any liquid goes in. Dry sugar keeps the cornstarch grains apart, so they do not clump when the milk hits them.

Whisk in the milk slowly until smooth, then add the egg yolks and the mashed banana and stir everything together. Everything starts cold, so there is no need to temper the yolks.

Set the pan over medium heat and stir constantly with a whisk or heatproof spatula, scraping the bottom and the corners. Nothing seems to happen for the first few minutes. Then, after about 6 to 8 minutes, the mixture thickens quickly into a custard that coats the back of a spoon.

Keep stirring as it starts to bubble gently, for about a minute. This matters more than it looks. Egg yolks contain an enzyme that breaks down cornstarch unless the custard gets hot enough, and a filling pulled off too early sets in the fridge and then turns thin overnight. When it is ready, the whisk leaves a trail that stays visible for a second.

Take the pan off the heat and stir in the butter and vanilla until melted and glossy. Add the heavy cream and the cinnamon or nutmeg now if you are using them. Pour the filling into a heatproof bowl, press plastic wrap directly onto the surface, cool it to room temperature, and chill for at least 2 hours until cold and set.

Filling a Banana Layer Cake Without Squeeze Out

This is a soft custard, not a frosting, so it needs a wall to hold it in. Level your cooled cake layers and put the first one on the plate. Pipe a ring of stiff frosting about ½ inch inside the edge, then spread the cold filling inside the ring. For an 8 inch cake, use the whole batch.

Set the second layer on top and press gently. Chill the cake for 30 minutes so the filling firms up before you frost the outside. Cream cheese frosting and whipped cream frosting both suit banana, and the cream cheese version makes a sturdier dam.

Because the filling is made with milk and egg yolks, keep the filled cake in the fridge and take it out about 30 minutes before serving.

Banana Filling vs Banana Pudding vs Banana Cream Pie Filling

They look alike in the bowl, but they are built differently. This banana filling cooks the mashed banana into the custard and uses only 1 cup of milk, so it sets firm enough to sit between cake layers.

Banana pudding is softer and spoonable, usually layered with wafers and sliced bananas. Banana cream pie filling is a vanilla custard with sliced bananas folded in after cooking, like the one in this banana cream pie. If you want a plain vanilla custard to pair with sliced bananas instead, use this vanilla pastry cream.

Thin, Lumpy or Gray: Saving the Filling

• Still runny after chilling: it did not bubble long enough. Return it to the pan, bring it back to a gentle bubble while whisking, and cook for a full minute.
• Lumpy or grainy: part of the custard set on the bottom of the pan, or a little egg cooked too fast. Whisk hard off the heat, or press it through a sieve before chilling.
• Gray on top: air reached the surface. Press the wrap right onto the filling and assemble the cake within a day for the brightest color.
• Tastes dull: stir in a few drops of lemon juice or a tiny pinch of salt.

Peanut Butter, Cocoa and Coconut Versions

Stir 1 tablespoon of peanut butter into the hot filling with the butter for a nutty version that goes well with chocolate cake. For a chocolate banana filling, whisk 1 tablespoon of cocoa powder in with the sugar and cornstarch.

Brown sugar instead of white gives a deeper, caramel flavor, close to this caramel cake filling. Coconut milk in place of the whole milk, with toasted coconut on the cake, turns it tropical.

Making Banana Filling Ahead

Make the filling up to 3 days before you need it and keep it in an airtight container with plastic wrap pressed on the surface. Stir it gently before using. It will be thick and firm from the fridge, which is what you want for filling a cake. Do not microwave it.

Freezing is not a good idea. Cornstarch custards weep when they thaw, and the banana turns the texture spongy and watery.

More Ways to Use Banana Cream Filling

Spread it between layers of a banana cake for a double banana cake, or between layers of a vanilla cake for a banana cream cake. Pipe it into cored cupcakes and top them with whipped cream, or spoon it into baked tart shells and add a few caramelized bananas on top.

It also works as a cold dip for crisp cookies.

Banana Cake Filling FAQ

Can I use this banana filling in cupcakes?

Yes. Cut a small cone out of each cooled cupcake, spoon or pipe in the cold filling, and frost over the top.

Why did my banana filling turn brown?

Banana darkens when air reaches it. The lemon juice slows this, and plastic wrap pressed on the surface keeps it pale for up to 3 days.

Can I add sliced bananas to the filling?

Yes, but add them only when you assemble the cake. Fresh slices release juice and brown, so they do not keep well in the stored filling.