Preheat your oven to 350°F (175°C). Grease and line three 8-inch round cake pans.

In a bowl, whisk together flour, baking powder, and salt. Set aside.

In a large mixing bowl, beat butter and sugar until light and fluffy.

Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.

Alternately add the dry ingredients and milk, starting and ending with the flour mixture.

Divide batter evenly into four bowls. Color each with pastel gel food coloring and swirl them gently together for a marbled effect.

Pour the batter into the prepared pans and bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.

Allow cakes to cool completely before frosting.

Beat butter until smooth. Gradually add powdered sugar, beating until fluffy.

Mix in heavy cream and vanilla extract until smooth.

Divide the frosting into separate bowls and tint each with food coloring.

Level the cake layers if necessary. Place the first layer on a cake stand and spread a layer of buttercream. Repeat with the remaining layers.

Apply a crumb coat and chill for 15 minutes.

Smooth the final coat of frosting using an offset spatula and bench scraper.

Pipe the unicorn mane using star and rosette piping techniques.

Roll out white fondant and shape into a spiral horn. Insert a dowel for support and dust with gold luster dust. Let it dry overnight.

Shape ears from fondant, adding a smaller pink piece inside.

Draw closed eyes with an edible black marker.

Attach the decorations to the cake using frosting.