Preheat an oven to 325 degrees and position on the lower and upper thirds. Line two baking sheets with parchment paper.

Pour the cooled melted butter into a large bowl. Using a whisk, add the sugar, egg and yolk, one at a time, until well combined. Whisk in the vanilla and set aside.

In a medium bowl, use a whisk to combine the flour, cocoa powder, salt and baking soda.

Using a silicone spatula, fold the flour mixture into the sugar-egg mixture, until thoroughly combined. Add the food coloring and mix until the color is uniform.

Wrap the dough with plastic wrap and refrigerate for at least 20 minutes.

Using a small ice cream scoop; form the dough into balls and place 2-inches apart onto the prepared baking sheets. Transfer the baking sheets to the oven and bake until the edges are light brown and the centers are still wet, about 14 to 16 minutes.

Immediately transfer the cookies to a wire cooling rack and let cool for 1 hour before serving or using with your ice cream sandwiches.