Rainbow Cake Funfetti Petit Fours with Vanilla Fondant Icing

With two layers of rainbow cake, a bright fondant icing, and oodles of colorful sprinkles, these bite-size Funfetti Petit Fours are ready to celebrate!

Sponge cake adapted from various versions of Molly Yeh’s Funfetti Cake Recipe.

Keyword cake, fondant, funfetti, icing, petit four, rainbow, sprinkles

Prep Time 40

Cook Time 20

Cooling time 30

Total Time 1

Servings bite size cakes

Ingredients

Funfetti Sponge Cake

1 ¼ cup all purpose flour
2 tablespoons cornstarch
½ teaspoon salt
1 teaspoon baking powder
½ cup 1 stick unsalted butter, room temperature (plus more for greasing the baking sheet)
¾ cup granulated sugar
2 egg whites
2 tablespoons vegetable oil
2 teaspoons vanilla extract
1/3 cup almond milk
1 cup artificially colored rainbow sprinkles, plus more for decorating
½ cup mixed berry jam

Vanilla Fondant Icing

6 cups powdered sugar
½ cup water
2 tablespoons light corn syrup
¾ cup white chocolate melting wafers
3-4 drops food coloring, blue or the color of your choice (optional)

Kitchen Supplies

9x13 inch non-stick baking sheet
Standing mixer or a hand mixer
Rubber spatula
Ruler

Instructions

Mix the Funfetti Batter

Heat oven to 350 degree F. Line a 9 inch by 13 inch non-stick baking sheet with a layer of parchment and then grease the parchment and any exposed pan thoroughly with butter.
Whisk together the dry ingredients (flour, cornstarch, salt, and baking powder) in a large bowl. Set aside.
In the bowl of a standing mixer, cream together the butter and granulated sugar until fully incorporated and very light and fluffy (about 5 minutes).
In a small bowl, beat the egg whites thoroughly with a whisk until they become frothy. This will aerate the egg whites for a lighter batter. Beat the aerated egg whites into the butter-sugar mixture one small tablespoon at a time, making sure the egg is fully incorporated before adding more. The batter should be very light and airy. Beat in the vegetable oil, vanilla extract, and almond milk one at a time.
Turning the mixer to low speed, mix the dry ingredients into the wet ingredients one cup at a time. Remove the bowl from the standing mixer and gently fold the rainbow sprinkles into the batter with a flexible rubber spatula. Be careful not to mix too rigorously, as doing so could break the air bubbles you’ve created with all of your mixing and whisking.
Pour the batter into the prepared baking sheet and spread it into a smooth, even layer. Bake 15-20 minutes, until the sponge cake is light golden in color and a toothpick can be inserted and come out clean. Allow the cake to cool, and then freeze for 30 minutes to overnight.

Cut and Assemble the Cake Layers

Once the sponge cake has chilled, invert the pan onto a large cutting board or other working surface, peeling off the parchment paper (you may need to loosen the edges where the cake meets the pan). With a large, sharp knife, cut off the ragged edges of the cake to leave a nice, clean edge. Using a ruler, cut the cake into uniform squares, 1 inch by 1 inch.
Match up the cake squares as best as you can. Place a very small dab of mixed berry jam on one square and press the second square on top of it, making a tiny cake “sandwich”. Repeat until all the cake squares are paired up. Arrange the cakes on a cooling rack set over a large piece of parchment paper, leaving a bit of space between.

Make the Fondant Icing

Bring a pot of water to a boil, and set a heatproof glass bowl over the pot to make a double boiler. Add the sugar, water, corn syrup, and vanilla extract to the bowl and carefully whisk them together until smooth (it should reach a temperature of about 92 degrees F). Stir in the white chocolate wafers until melted and smooth.
Careful not to burn yourself, remove the glass bowl from the pot of boiling water and set on a trivet or folded kitchen towel. If you want a colored fondant, add a few drops of your chosen food coloring a little at a time until you achieve the desired shade of icing (I like to add 3-5 hearty drops for a nice dark color).

Assemble the Petit Fours

Prepare your work station next to the cooling rack of tiny cakes. You'll want a few bowls of different decorating sprinkles, the bowl of fondant icing, and a spoon.
While the fondant icing is still warm, pour spoonfuls over the cakes, letting the icing drip over the sides and onto the parchment underneath. You can try to cover the cakes completely, or just do a partial “drape” of icing, like the majority of the petit fours pictured here. Work quickly and in batches, decorating with sprinkles as you go. The icing should smooth out and cool quickly.
Leave the decorated Funfetti Petit Fours to set for 20-30 minutes. Store in a single layer in a sealed container for 2-3 days, or in the refrigerator for 4-5 days. Serve arranged on a pretty platter with tea, coffee, and probably a good number of lacy doilies for good measure.

Notes

The Lightest, Fluffiest Batter: The recipe here is formulated to make a very pale, very light sponge cake. The key to the color is to use only the lightest white ingredients (egg whites, white flour, white sugar, etc.). The key to the texture is in aerating the batter as much as possible - whisking the egg whites until frothy and creaming the butter and sugar until fluffy. Avoid using a rigid spoon when mixing in the sprinkles, as a flexible spatula is less likely to break the air pockets you've painstakingly created.

Artificially Colored Sprinkles Only: The natural kind just won't "bleed" dye like the processed ones.

Pouring on the Fondant Icing: The icing will start to harden quickly. Work in batches, sprinkling the decorating sprinkles before it dries so that they stick. Once complete, don't move until the icing has fully hardened or you may leave fingerprints.