- Preheat the oven to 350°F. Grease a 9x13-inch baking pan or line it with parchment paper for easy removal. 
- In a medium saucepan, melt the butter over low heat. Once melted, remove from heat and stir in the granulated sugar until well combined. Allow the mixture to cool slightly. 
- Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract. 
- In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix. 
- Fold in the chocolate chips and crushed chocolate sandwich cookies until evenly distributed. 
- Pour the brownie batter into the prepared baking pan, spreading it evenly. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. 
- Allow the brownies to cool in the pan on a wire rack for at least 15 minutes before cutting into squares.