Preheat oven to 350°F (175°C). Grease two 8-inch cake pans, line with parchment, and dust with flour.

In a bowl, whisk cake flour, baking powder, and salt until combined.

In a large bowl, beat butter and sugar with an electric mixer until fluffy (about 3 minutes). Add eggs one at a time, then vanilla extract, mixing well.

Gradually add dry ingredients and milk to the wet mixture, alternating (start and end with dry). Mix until just combined.

Divide batter into two equal portions. Add pink or blue food coloring to one portion, leaving the other plain or neutral.

Pour each batter into a prepared pan. Bake for 25-30 minutes, or until a toothpick inserted comes out clean. Cool in pans for 10 minutes, then transfer to a rack.

For frosting: Beat 1 cup butter until creamy (2 minutes). Gradually add powdered sugar, then heavy cream and vanilla, whipping until light and fluffy (3-4 minutes).

Assemble: Place the plain cake layer on a plate. Spread a thin layer of frosting, then carve a 2-inch circle in the center. Fill with colored frosting or sprinkles.

Top with the colored cake layer. Frost the entire cake with a neutral color (e.g., white). Decorate as desired.

Chill for 30 minutes to set, then slice to reveal the surprise!