01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper and set aside.
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 - Add egg yolk, milk, vanilla extract, and red food coloring to the butter mixture. Beat until fully incorporated and uniform in color.
05 - Gradually mix in the dry ingredient mixture on low speed until just combined. Avoid overmixing to prevent tough cookies.
06 - In a small separate bowl, whisk together softened cream cheese, powdered sugar, and vanilla extract until smooth and creamy. Set aside until ready to use.
07 - Roll dough into 1-inch balls, approximately 24 cookies total. Place on prepared baking sheets, spacing 2 inches apart to allow for spreading.
08 - Using your thumb or the back of a teaspoon, gently press a deep indentation into the center of each dough ball, being careful not to press through to the baking sheet.
09 - Spoon approximately 1/2 teaspoon of the cream cheese filling into each indentation, mounding slightly above the cookie surface.
10 - Bake for 11 to 13 minutes, or until edges are set and centers are slightly puffed. The filling may still appear soft but will firm upon cooling.
11 - Let cookies cool on the baking sheet for 5 minutes to set. Transfer to a wire rack and cool completely before serving or storing.