01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.
03 - In a large bowl, cream butter and sugar together until light and fluffy, about 2 minutes.
04 - Add egg yolk, milk, vanilla, and red food coloring. Beat until fully combined.
05 - Gradually mix in the dry ingredients until just combined. Do not overmix.
06 - In a small bowl, whisk together cream cheese, powdered sugar, and vanilla extract until smooth. Set aside.
07 - Roll dough into 1-inch balls, yielding approximately 24 cookies. Place on baking sheets, spacing 2 inches apart.
08 - Using your thumb or the back of a teaspoon, gently press an indentation into the center of each ball.
09 - Fill each indentation with about 1/2 teaspoon of the cream cheese filling.
10 - Bake for 11–13 minutes, or until edges are set.
11 - Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.