Step 1: Make the Brownies

1. Preheat oven to 350°F (175°C) and line an 8×8-inch pan with parchment paper.
2. In a bowl, whisk together melted butter and sugar until smooth.
3. Add eggs and vanilla extract, mixing well.
4. Stir in flour, cocoa powder, salt, and baking powder until just combined.
5. Pour batter into the prepared pan and bake for 20-22 minutes or until a toothpick comes out with a few moist crumbs.
6. Let the brownies cool completely before adding the cookie dough layer.

Step 2: Prepare the Cookie Dough

1. Heat-treat the flour by microwaving it for 30-60 seconds or baking at 350°F (175°C) for 5 minutes. Let cool.
2. In a bowl, beat butter, brown sugar, and granulated sugar until fluffy.
3. Mix in milk and vanilla extract.
4. Gradually add flour, mixing until smooth.
5. Fold in mini chocolate chips.

Step 3: Assemble the Layers

1. Spread the cookie dough mixture evenly over the cooled brownie layer.
2. Refrigerate for 30 minutes to firm up.

Step 4: Add the Chocolate Topping (Optional)

1. Melt chocolate chips and butter together until smooth.
2. Drizzle or spread over the cookie dough layer.
3. Refrigerate for another 15-20 minutes until set.

Step 5: Slice & Serve

1. Cut into squares and enjoy chilled or at room temperature!