Beat the butter and sugar until light and fluffy, about 2 to 3 minutes. Mix in the egg, vanilla, and green gel food coloring until evenly combined.

Whisk the flour, baking powder, and salt, then stir into the wet mixture. Shape the dough into a disc, wrap, and chill at least 1 hour.

Heat oven to 350°F. Roll dough into 24 balls, place on parchment-lined sheets, and bake 8 to 10 minutes until edges are set.

Press a red heart candy into the center of each warm cookie. Cool on the sheet for 2 minutes, then transfer to a wire rack.