In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.

In a large bowl, beat softened butter and sugar with an electric mixer until light and fluffy (2-3 minutes). Beat in the egg and vanilla. Mix in the lime green gel food coloring until the color is vibrant and uniform.

Add the dry ingredients to the wet and mix on low speed until just combined. Do not overmix. Cover the soft dough and chill in the refrigerator for at least 1 hour.

Preheat oven to 350°F (175°C). Line baking sheets with parchment paper. Place powdered sugar in a small bowl. Scoop chilled dough into 1-inch balls, roll until smooth, then coat generously in powdered sugar.

Place dough balls 2 inches apart on baking sheets. Bake for 10-12 minutes, until edges are set but centers are soft. Immediately press one red heart sprinkle into the center of each hot cookie. Cool on the baking sheet for 5 minutes before moving to a wire rack.