In a large bowl, beat the butter and 3-4 drops green food coloring together with an electric mixer (or stand mixer) on medium speed for approximately one minute until combined well.
Add the sugar, vanilla extract and the egg yolk and beat to until mixed thoroughly.
Gradually add in the flour and baking powder and mix until just barely combined, scraping down the sides of the bowl as you mix.(be careful not to over-mix).
Place the dough in the freezer for 15 minutes to chill for easier rolling.
Roll out the dough on a lightly floured surface until approximately ¼ inch thick.
Then cut out 2” circles with round cookie cutter (or a top of a mason jar) and place them on a baking sheet lined with parchment paper.
While the dough is in the freezer, preheat the oven to 350° F.
Bake the cookies for 13-15 minutes or until the edges are golden brown, careful not to over-bake.
Remove the cookies from the oven and immediately press a candy heart into the center of each cookie.
Let the cookies cool on a baking sheet for 5 minutes then transfer to a wire rack to cool completely