Preheat oven to 350 degrees F. In a small bowl, whisk together flour, cocoa, baking soda and salt. Set aside.
In the bowl of an electric mixer, beat together butter and sugar until fluffy, about 5 minutes. Add in the cream cheese and beat until combined (it’s okay if small clumps form), then beat in the egg yolk and vanilla extract. With the mixer on low speed, beat in the dry ingredients until combined. Use a spatula to stir in the chocolate chips.
Refrigerate the dough for 10 to 15 minutes, just until it’s slightly less sticky and easier to roll into balls. Roll into golf-ball sized balls and place about 2 inches apart on a nonstick baking sheet. Bake for 12 to 15 minutes, or until the cookies are set. Let cool completely before covering in the glaze.
Whisk together all the ingredients until smooth and creamy. Use a spoon or spatula to spread the glaze on the cookies or use a pastry bag (I did!) to pipe it across.