Preheat the oven to 350°F (175°C). Line a small baking sheet with parchment paper or a silicone baking mat.

In a bowl, stir together the melted butter, granulated sugar, egg yolk, vanilla extract, and red gel food coloring until combined.

Evenly sprinkle the all-purpose flour, unsweetened cocoa powder, baking soda, and fine salt over the wet mixture, then gently stir just until combined.

Press the dough flat and divide it into two equal halves, rolling each portion into a ball and then rolling in extra granulated sugar.

Place the sugar-coated dough balls evenly spaced on the prepared baking sheet.

Bake in the preheated oven for 10-12 minutes until the cookies have spread and started to crackle on top.

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

Once cooled for about 10 minutes, gently press a white chocolate peanut butter heart into the center of each cookie.

Place the cookies in the refrigerator for 30 minutes to allow the white chocolate hearts to set.

Remove cookies from the fridge and bring them to room temperature before serving.