Preheat the oven to 350°F and line a small baking sheet with parchment paper (or use 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 in the bowl and divide it in half. You should get 3 cookies from each half.

Roll each dough ball in your hands, then lightly roll in extra granulated sugar. Space 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 the cookies have cooled for 10 minutes, press a white chocolate heart into the center of each cookie.

Move the cookies to the fridge to set for 30 minutes.

Bring to room temperature before serving.