In a medium mixing bowl, combine flour, cocoa mix, baking soda, baking powder, and salt; set aside.

In a large mixing bowl beat together butter and sugar on medium speed. Add eggs, milk, and vanilla; beat until fully incorporated. Mix in dry ingredients, in two additions, until just moistened.

Preheat oven to 350 degrees F. While oven heats, place cookie dough in the refrigerator. Th dough will be tacky when it’s finished, chilled the dough makes it easier to roll. Keep the dough in the fridge in between baking to help keep it easy to roll.

Scoop out cookie dough by the tablespoon and roll into a ball. Bake for 10 to 12 minutes, until edges just being to brown. Leave cookies on pan for one minute then transfer to a wire rack to cool completely.

In a large mixing bowl, beat cream cheese until smooth on medium-high speed.

Add corn syrup, sugar, and vanilla. Beat until combined. Add Greek yogurt and beat until smooth.

Pair up your cookies so they are about the same size as their partner. Using an offset spatula (or regular spatula) place about 2 tablespoons of filling on the bottom of one cookie. Spread the filling over the cookie, all the way to the edges. Top with second cookie (bottom side touching the filling) and squeeze a little to secure everything.

Place finished sandwich cookies on a baking sheet. Refrigerate cookies for at least 1 hour before serving so the filling can fully set.