Preheat oven to 350 degrees and line two cookie sheets with parchment paper.
Using a medium bowl, whisk the flour, cocoa powder, baking soda, and salt until combined.
Using a standing mixer, beat the butter, brown sugar, sugar, eggs, vanilla, and red gel food coloring until combined and fluffy.
Gradually beat in the dry ingredients until a dough forms.
Pour the red sanding sugar into a small bowl.
Using a tablespoon, scoop some dough into your hands and roll it into a ball.
Roll the dough into the red sanding sugar.
Place the dough ball onto the cookie sheets, about 12 cookies per sheet.
Bake in the oven for 10-12 minutes or until set around the edges.
Remove from the oven and allow to cool for 1 minute before placing a chocolate heart into the center of the cookies.
Allow cooling completely before enjoying!