Preheat the oven to 350°F and line a small baking sheet with parchment paper.

Stir together the melted butter, granulated sugar, egg yolk, vanilla extract, and red food coloring until well combined.

Sprinkle the flour, cocoa powder, baking soda, and salt evenly over the dough, and stir just to combine.

Press the dough flat in the bowl, divide it in half, and shape into 6 cookies.

Roll each dough ball in hands and then in extra granulated sugar before placing evenly on the prepared baking sheet.

Bake for 10-12 minutes, until they spread, start to crackle, and appear dry on top.

Let the cookies rest on the baking sheet for 2 minutes before transferring them to a wire rack to cool completely.

After cooling for 10 minutes, press a white chocolate heart into the center of each cookie and place in the fridge to set for 30 minutes.

Bring to room temperature before serving.