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

Stir together the melted butter, 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 and divide it in half; form three cookies from each half.

Roll each dough ball in your hands, then roll lightly in extra granulated sugar, and space them 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 moving 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 move to the fridge for 30 minutes to set.

Bring to room temperature before serving.