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.