#### **Make the Brownie Layer**
**Preheat the Oven**
Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, leaving some overhang for easy removal.
**Mix the Brownie Batter**
In a large mixing bowl, whisk together the melted butter and sugar until smooth. Add the eggs and vanilla extract, whisking until combined.
**Add Dry Ingredients**
In a separate bowl, mix the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the wet ingredients, stirring until just combined.
**Assemble the Layers**
Pour the brownie batter into the prepared pan, spreading it evenly. Place whole Oreos on top of the batter, pressing them slightly into the mixture.
**Bake**
Bake for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Let the brownies cool completely before adding the cookie dough layer.
#### **Make the Cookie Dough Layer**
**Cream the Butter and Sugar**
In a mixing bowl, beat the softened butter, brown sugar, and granulated sugar until light and fluffy. Add the milk and vanilla extract, mixing well.
**Add Flour and Chocolate Chips**
Gradually mix in the flour and salt until well combined. Stir in the mini chocolate chips.
**Spread Over Brownies**
Once the brownies are completely cooled, spread the cookie dough evenly over the top. Use a spatula to smooth it out.
**Chill and Serve**
Refrigerate for at least 1 hour to set before slicing into squares. Enjoy!