Instructions
- 1
Make vanilla batter. Divide equally into 5 bowls.
- 2
Color each batch a vivid rainbow color using gel food coloring.
- 3
Bake each layer at 350°F for 20-22 minutes. Cool completely.
- 4
Make white vanilla buttercream: beat butter pale, add powdered sugar and cream.
- 5
Stack layers in rainbow order (red-orange-yellow-green-blue) with thin buttercream between each.
- 6
Apply a smooth crumb coat. Refrigerate 30 minutes.
- 7
Apply final thick coat of white buttercream all over.
- 8
While still soft, press rainbow sprinkles all over the sides. Pipe rosettes on top. Add more sprinkles.
Baker's Tip
Gel food coloring is essential — liquid food coloring adds too much liquid and creates uneven color. Use a separate spatula and bowl for each color and make the colors bolder than you think you need — colors fade slightly during baking.
Frequently Asked Questions
Why do you use gel food coloring rather than liquid?
Gel coloring is far more concentrated — a tiny amount creates vivid color without adding the liquid that liquid dyes introduce. Excess liquid changes the batter consistency, can create a gummy texture, and makes the colors dull. Gel gives bold, true colors with just a few drops.
How do I bake 5 layers without 5 pans?
Bake in batches — most ovens can handle 2-3 pans at once. Rotate pans halfway through for even baking. The batter is stable enough to sit at room temperature for 20 minutes while waiting for the oven. Keep unbaked batter covered with plastic wrap.
The layers keep sliding when I try to stack them — what do I do?
Insert 3-4 wooden dowels or drinking straws through the stacked layers to anchor them. Alternatively, refrigerate between each layer addition for 10 minutes to let the buttercream set firm before adding the next. Use a very cold, stiff buttercream for the layers.
Can I make this as a two-tier cake?
Yes — make a 6-inch two-tier version for a dramatic tall rainbow cake. Use a full recipe for the bottom tier (4-inch layers) and half a recipe for the top tier. Insert wooden dowels in the bottom tier to support the weight before stacking.
About This Recipe
The ultimate birthday cake — five vivid rainbow-colored layers of moist vanilla sponge, each a different color of the spectrum, frosted with pure white vanilla buttercream and covered in rainbow sprinkles. The cross-section is pure joy.
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