1. Prepare the Dough:

• Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
• In a large mixing bowl, cream together the softened butter and brown sugar until light and fluffy.
• Add the egg yolk and vanilla extract, mixing until well combined.
• In a separate bowl, whisk the flour and cocoa powder. Gradually add this dry mixture to the wet ingredients, stirring until a dough forms.
• Add the red food coloring and mix until the color is evenly distributed.

2. Shape the Cookies:

• Roll the dough into 1-inch balls and coat each ball in granulated sugar or sanding sugar.
• Place the balls on the prepared baking sheets, spacing them 2 inches apart.
• Use your thumb or the back of a spoon to gently press an indentation into the center of each dough ball.

3. Make the Cream Cheese Filling:

• In a medium bowl, beat the softened cream cheese, egg yolk, sugar, salt, and vanilla extract until smooth and creamy.

4. Assemble and Bake:

• Spoon a small amount of the cream cheese filling into the indentations of the cookies, filling them almost to the top.
• Bake in the preheated oven for 12-14 minutes, or until the edges of the cookies are set and the filling is slightly puffed. Avoid overbaking.

5. Cool and Serve:

• Let the cookies cool on the baking sheets for a few minutes, then transfer them to a wire rack to cool completely.
• Serve fresh or store in an airtight container in the refrigerator for up to 5 days.