In a mixing bowl with the paddle attachment, beat the softened butter and sugar together until light in color.
Add in the egg, vanilla and milk and continue to beat.
In a separate bowl, combine flour, baking powder and salt.
Gradually add the flour mixture into the butter mixture with the mixer on low speed.
Scrape the sides and bottom of the bowl and mix until combined, but don't over mix. Just until the ingredients are together.
Roll the dough in a ball and refrigerate for 20 minutes so it firms up a little and is easier to cut the shapes from.
Prepare two (or three) cookie sheets with parchment paper and preheat the oven to 375 degrees.
Remove dough from the fridge and make a space on the counter to roll it out. Use powdered sugar rather than flour when rolling the cookies so they don't stick to the surface. You can use the sugar on the top and bottom of the dough and the rolling pin. Roll to about 1/4 to 1/2" thick.
Cut out little heart shapes with a tiny 1" heart cookie cutter. This recipe make a lot of hearts, so you'll need to bake a few batches! Place them on the cookie sheet, about 1/2" apart.
Bake in the oven for 7 minutes or until cookies are just about to turn golden brown.
Remove and let them cool before you frost!