Preheat oven to 350°F. Line a cupcake pan with cupcake liners. Prepare the Betty Crocker Supermoist butter-recipe yellow cake mix according to the package directions and bake the cupcakes as directed on the package. Let cupcakes cool completely.
To make the cookie dough filling, with a mixer cream together 1/2 cup unsalted butter and 3/4 cup light brown sugar at medium speed. Add 1 teaspoon vanilla extract and beat well. Add 1 1/4 cup flour and 1/2 teaspoons salt and mix until combined. Add 2-4 Tablespoons milk gradually until the desired consistency is reached and beat until fluffy. Gently fold in 1 cup mini chocolate chips. Chill the cookie dough mixture in the refrigerator until firm.
To make the wells, cut a cylinder-shaped portion out of the center of each cooled cupcake using an apple corer; an apple corer works great and the removed cake can be eaten.
Fill each hole with a chunk of the chilled cookie dough mixture so the center is filled but not overflowing.
Frost the cupcakes with chocolate frosting. For a piped cone shape, put the frosting in a plastic storage bag and snip off a nickel-sized hole in one corner to pipe the frosting on.
Garnish the frosted cupcakes with mini chocolate chips and, if desired, mini chocolate chip cookies.
To make mini cookie garnishes (optional), use 1/4 package refrigerated cookie dough: place nickel-sized balls of dough on a cookie sheet and bake at 350°F for 8-9 minutes, then cool and use to top the cupcakes.