In a small bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large bowl, beat the softened butter, sugar and vanilla extract until creamy. Pour in the eggs and mix well.
Mix in dry ingredients in 2 batches, alternating with milk.
Fold in the pretty blue and pink sprinkles. Mix all ingredients until well combined.
Place cupcake liners in the 12-cup cupcake pan.
Bake for 25 minutes. Check with a toothpick to see if the cake part is baked through. When the cupcakes come out of the oven, let them cool completely.
To make the icing:
Beat the butter, salt, and powdered sugar on low until it’s all combined. Add vanilla extract and beat on medium-high speed until creamy. About 3 minutes. Beat in milk on medium-high speed for 1 minute, or until fluffy.
Place 1/2 cup of the plain icing in a small bowl. Stir in a small amount of blue or pink gel food coloring until the icing is the desired color.
Keep your cupcakes in the pan and cut a small hole on the top of the cupcake, right in the center. This will be filled with blue or pink icing. I used a Wilton 1A icing tip to punch a hole.
Fill the hole with the icing and place the portion of the cutout cupcake back over the top.
Pipe plain icing on top and decorate with sprinkles before serving.
Be sure to let cupcakes cool completely before taking steps to add the filling.