Preheat oven to 350°F. Line a regular cupcake pan with 8 paper liners. 

In a glass measuring cup, heat milk until steaming. Add 1oz chocolate to warm milk, stirring until melted. Set aside. 

In a large bowl or stand mixer, beat together butter and sugar until light and fluffy. Mix in egg and vanilla, scraping bowl as needed. Mix in salt, baking soda and cocoa powder, followed by flour. Mix in sour cream, followed by warm milk mixture. Mix until just combined and no streaks remain. Divide mixture between prepared liners using a large cookie scoop. Bake for 18-20 minutes or until a toothpick inserted comes out clean or with just a few moist crumbs. Cool in pan for several minutes, then transfer to a wire rack to cool completely. 

When cupcakes are cool, prepare frosting. In a large bowl or stand mixer, beat together cream cheese and butter until smooth. Add vanilla. Mix in powdered sugar 1 cup at a time. Finally, stir in cookie crumbs by hand, mixing until just combined. Transfer to a large piping bag fit with desired tip. Frost cupcakes and immediately top off with a cookie. 

Cupcakes can be stored in the refrigerator. Bring to room temperature prior to serving.