01 - Preheat 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 until well blended.
03 - In a large bowl, beat softened butter and granulated sugar with an electric mixer until light and fluffy, approximately 2 minutes.
04 - Mix in egg yolk, milk, vanilla extract, and red food coloring. Beat until fully incorporated and uniform in color.
05 - Gradually add dry mixture to wet ingredients, mixing on low speed just until combined. Avoid overmixing to prevent tough cookies.
06 - In a small bowl, whisk softened cream cheese, powdered sugar, and vanilla extract until smooth and creamy. Set aside.
07 - Roll dough into 1-inch balls, yielding approximately 24 cookies. Arrange on prepared baking sheets, spacing 2 inches apart.
08 - Gently press your thumb or the back of a teaspoon into the center of each dough ball to create a well for the filling.
09 - Spoon about 1/2 teaspoon of prepared filling into each indentation, being careful not to overfill.
10 - Bake for 11 to 13 minutes, or until edges are firm and set. Centers should still appear slightly soft.
11 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack to cool completely before serving.