• Preheat the oven to 300 degrees.
• Line a baking sheet with parchment paper and set aside.

For the Filling:

• In a medium size bowl with an electric mix together cream cheese, and sugar until well blended. Add in salt, vanilla, egg yolk, and sour cream, continue mixing until everything is evenly mixed. Cover the bowl and place in the refrigerator for at least 30 minutes.

For the Cookies:

• In a medium bowl combine flour, cocoa powder and salt, mix until well incorporated.
• In the bowl of a stand mixer fitted with a paddle attachment cream together butter and sugar.
• Add in egg yolk and vanilla and continue mixing until well incorporated.
• Add the flour mixture in gradually, mixing after each addition, until it's all added.
• Add in about 1/8 teaspoon of red gel food coloring and continue mixing until it the color is evenly distributed.
• Add more food coloring if a deeper color is desired.
• Place red sanding sugar in a shallow dish.
• Scoop out dough in tablespoon-size scoops and roll into balls.
• Roll the dough balls in the sanding sugar to evenly coat them.
• Place on the prepared cookie sheet.
• Using the handle of a wooden spoon, your finger, or another small round object press a hole in the center of each dough ball.
• Bake for 10 minutes.
• Remove from the oven, gently press the center of each cookie again and fill with the cream cheese filling.
• Place back in the oven and bake 10-12 minutes or until the filling is set.
• Allow to cool on the baking sheet for 2-3 minutes before removing to a wire rack to cool completely.
• Store in an airtight container.