Follow box cake directions EXCEPT use an equal amount of butter instead of oil.
Cook until toothpick comes out clean.
Make your favorite buttercream recipe. I used 2 large batches.
Stack each cake layer with about 1/4 inch of frosting between each layer. Make sure your frosting is smooth and even.
Frost the outside of the cake. Use a generous amount so that cake crumbs don't mix with the frosting.
Add your unicorn cake topper and eyelashes.
Rainbow Piping Bag & Flowers
Separate the rest of the frosting equally into 5 bowls and add food coloring. I did pastels - pink, orange, yellow, green, blue.
Using a piping bag, pipe pink circles for the cheeks. You can press edible glitter onto the cheeks if you like.
Lay out a sheet of plastic wrap. Starting at the edge, use a spatula to make lines of each color frosting. Then, roll up the plastic wrap and twist the edges to create a tube.
Cut one end of the tube and place in your piping bag with a large star tip.
Keeping the piping bag close to the cake, guide the bag in spirals to create flowers. Fill in the holes with stars.