Preheat oven to 350 degrees.  Line mini muffin pans with mini paper liners.  Set aside.

In a large bowl, using a handheld mixer, mix together the butter and sugar on medium speed for 3 minutes.

Add the eggs one at a time and blend well into the sugar and butter mixture.

Next, add the vanilla and mix into the batter.

Scrape down the bowl and add the following ingredients in this order: flour, baking powder, and salt. Using the mixer, on low speed, gently blend the baking powder and salt into the flour - just a few seconds.  Now, increase the speed on the mixer to medium and blend the flour into the batter just until the flour is incorporated.

Add the milk and fully incorporate.

Divide the batter into four separate bowls.  Add a very small amount of food colouring gel to each bowl.  I use a toothpick for each colour to keep them separate.

Stir the food colouring gel into the batter until well incorporated.  (Add more colouring or less so that you achieve the desired colour to fit your personal tastes.)

Place 1 heaping teaspoon of batter into each mini muffin paper liner.  You may have to do this in batches depending on the size of your mini muffin pans.

Bake for 15 minutes.  Remove from oven and allow to cool completely on a wire cooling rack.

When cooled, top with buttercream frosting and candy sprinkles.  (I used an Open Star Tip #68.)  Enjoy!