Preheat oven to 325º F. Generously butter an 8-inch square metal baking pan. Add a layer of parchment paper, leaving the edges long enough to lift the brownie bites out of the pan for easier slicing. Press the parchment down to help it adhere smoothly to the pan. Set aside.

For the brownie layer, combine butter, sugar, cocoa powder, and salt in a medium bowl. Stir until well combined; the mixture will be very thick. Add vanilla and egg and mix well. Add flour and stir until combined. Spread the batter into a thin layer on the bottom the prepared pan (fingers work best to spread the thick, gooey mixture as evenly as you can). Bake until set, about 15 to 20 minutes. Cool to room temperature.

Once the crust is cool, prepare the cookie dough filling. Beat butter, sugars, and salt on medium speed in the bowl of a standing electric mixer until light and fluffy. Add vanilla and cream and mix well. Add flour and mix on low speed until incorporated. Stir in chocolate chips briefly on low speed or mix in by hand.

Spread the cookie dough filling over the brownie, using a the back of a spoon or an offset spatula to create an even layer. Smooth the top as best as you can. Set aside and prepare the ganache (if not preparing ganache right away, refrigerate until ready).

Place chopped chocolate in a measuring glass with a pour spout; set aside. In a small saucepan, bring cream to a boil over medium heat. Pour hot cream over the chocolate; without stirring, let the cream-chocolate mixture sit for 2 minutes. After 2 minutes, stir slowly with a rubber spatula until the mixture is smooth and glossy.

Acting quickly, pour ganache over the cookie dough filling. Carefully pick up the pan, tilting and rotating to spread the ganache to the edges as needed. If desired, pop any large bubbles that form with a toothpick or the tip of a sharp knife.

Refrigerate uncovered until set, at least 30 minutes. Slice in 1 to 2-inch squares. Serve chilled.