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Rainbow Cake

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  • Author: Fadela
  • Total Time: 1 hour
  • Yield: 8 - 10 slices

Description

A colorful rainbow layer cake with six fluffy sponges, filled with light mascarpone whipped cream, covered in buttercream frosting, and decorated with a colorful drip. (For a 6-inch cake – about 8 to 10 servings)

Ingredients

White Cake Layers

  • 3 ¼ cups (415 g) cake flour 
  • 2 ½ tsp (11 g) baking powder
  • ¾ tsp (4 g) baking soda
  • ½ tsp salt
  • 1 cup (225 g) unsalted butter, softened
  • 1 ¾ cups (370 g) granulated sugar
  • 6 large egg whites (about 210 g)
  • 1 ⅓ cups (330 ml) buttermilk
  • 3 tsp vanilla extract
  • Gel food coloring: red, orange, yellow, green, blue, purple

Mascarpone Whipped Cream Filling

  • 7 oz (200 g) mascarpone cheese, chilled
  • 1 ¼ cups (300 g) heavy cream, cold
  • 3 tbsp powdered sugar
  • 1 tsp vanilla extract

Buttercream Frosting

Follow my American Buttercream Frosting recipe

Rainbow Drip

  • 4 ¼ oz (120 g) white chocolate, finely chopped
  • 3 tbsp (45 ml) heavy cream
  • Gel or oil-based food coloring: red, orange, yellow, green, blue, purple

Instructions

For the Cake Layers

  1. Preheat the oven to 325°F (160°C), convection/fan. Grease and line the bottoms of six 6-inch (15 cm) round cake pans with parchment paper.
  2. In a large mixing bowl (or the bowl of a stand mixer), beat the softened butter and granulated sugar until light and creamy.
  3. Add the egg whites gradually along with the vanilla extract, mixing well after each addition until the batter is fluffy.
  4. Using a spatula, gently fold in the sifted flour, baking powder, baking soda, and salt, alternating with the buttermilk, until the cake batter is smooth and well combined.
  5. Divide the batter evenly into six bowls using a kitchen scale.
  6. Tint each portion with gel food coloring (red, orange, yellow, green, blue, violet) and stir until the color is fully incorporated.
  7. Pour the colored batters into the prepared cake pans and bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean.
  8. Let the cakes cool in the pans for 5 minutes, then remove and transfer to a wire rack to cool completely.

For the Buttercream Frosting

Prepare the buttercream following my American Buttercream recipe and set aside.

For the Mascarpone Whipped Cream

  1. In a chilled mixing bowl, whip the cold heavy cream, cold mascarpone, powdered sugar, and vanilla extract together until stiff peaks form.
  2. Keep refrigerated until ready to assemble.

To Assemble the Layer Cake

  1. Place the purple sponge layer on a cake board set on a turntable.
  2. Spread an even layer of mascarpone whipped cream with an offset spatula, then top with the blue sponge.
  3. Repeat with the green, yellow, and orange layers, finishing with the red layer on top. (Chill for 20 minutes if needed to stabilize.)
  4. Cover the cake with a thin crumb coat of buttercream frosting, smooth, and refrigerate for 30 minutes.
  5. Add a second, thicker layer of buttercream, smooth with a cake scraper, and chill until firm to the touch.

For the Drip and Decoration

  1. Melt the white chocolate and heavy cream together in the microwave or over a double boiler until smooth and fluid.
  2. Divide into six small bowls, tint with gel food coloring, and let cool to about 86°F (30°C) before using.
  3. Drip the colorful ganache around the edges of the chilled cake.
  4. Finish by piping buttercream swirls on top and sprinkling with rainbow sprinkles.
  5. Serve the rainbow layer cake, or refrigerate and bring to room temperature for at least 30 minutes before slicing.

Equipment

Notes

Storage:  This rainbow cake keeps well for up to 2 days in the refrigerator, covered with a cake dome or stored in an airtight container. Bring it out at least 30 minutes before serving so the cream softens back to the right texture.

Tips:

  • The cup measurements are approximate. For best results in baking, always use a kitchen scale instead of relying only on cups.
  • Use gel food coloring (brands like Wilton, Americolor, or Rainbow Dust) for vibrant colors that stay bright after baking.
  • Weigh each portion of batter to get even, consistent cake layers.
  • Level the sponges with a cake leveler or a large serrated knife for a clean assembly.
  • Assemble inside a tall acetate cake collar (or a deep cake ring) to keep the layers stable.
  • Chill the cake between steps of frosting and decorating—this makes smoothing and adding the drip much easier.
  • Prep Time: 40 minutes
  • Cook Time: 20 minutes
  • Category: cake, layer cake
  • Cuisine: American

Find it online: https://sweetlycakes.com/en/rainbow-cake/