Line an 8 x 8 pan with parchment paper leaving an overhang on two sides. Pre-heat the oven to 350 degrees Fahrenheit.
Melt the butter in a small saucepan on medium low heat until it turns a golden-brown color and has a nutty smell, about 5-7 minutes. It will foam up during this time so keep stirring and checking the color under the foam. Once it starts to turn color, don't walk away as it can burn quickly. Remove from the heat and cool for 5 minutes.
Add the melted butter and brown sugar to a medium bowl and stir until combined. Add the eggs and vanilla and mix well.
Stir in the cookie butter.
Add the flour, baking powder and salt and stir until just combined, leaving some streaks of flour visible. Add the crushed cookies and stir gently until distributed throughout the batter and the flour is absorbed. Be careful not to overmix.
Pour the batter into the prepared pan and smooth the top. Sprinkle more crushed cookies on top if desired.
Bake for about 20-25 minutes until the edges are golden and the middle feels almost set. Cool completely before cutting.