Preheat oven to 350 degrees and spray a petit four baking pan with pam baking spray
Using a large bowl, whisk until combined the eggs, oil, and milk until combined and smooth
Divide the batter into four bowls
Mix in the pink, blue, and purple gel food coloring into their own bowls, leaving the 4th bowl color free
Spoon 1 tsp of each batter into the petit four cavities
Bake in the oven for 15 minutes or until a toothpick comes out clean
Remove from the pan and place onto a wire rack
Allow the petit four to cool completely
Using one of the vanilla frosting containers, scoop into a medium bowl
Microwave for 15 - 20 seconds or until the frosting is liquid-like
Carefully pour the frosting over the petit fours to completely coat the cakes
Allow the frosting to firm up.
Using 4 bowls, spoon about 1⁄4 C of the second frosting container into each bowl
Mix in a few drops of each color into their own bowl and mix until the colors are combined
Scoop the pink and blue frosting into the piping bag fitted with the star tip
Scoop the purple and the black frosting into the piping bag fitting with the number 2 tip
Using the pink and blue frosting, pipe “hair” onto the unicorn
Using the purple frosting, pipe little dots into the “hair”
Using the black frosting, pipe details of the eyes on the front of the petit four
Carefully place the unicorn horn sprinkle onto the top center of the petit four
Allow the frosting to firm up for 30 minutes before enjoying!