Preheat your oven to 350 degrees. Grease a 9x13 inch baking dish and set aside.

In a large bowl, whisk together the melted butter and brown sugar until a paste forms. Allow to cool slightly, about 5 minutes.

Mix in the beaten eggs and vanilla extract.

In a medium bowl, mix together the flour, chocolate chips, baking powder, salt, and baking soda.

Slowly mix the flour mixture into the butter mixture, adding just 1/3 of the flour at a time until fully combined.

Pour the cookie bar batter into the greased baking dish.

Sprinkle the mini peanut butter cups and chopped chocolate cookie sandwiches over the top of the cookie batter. Gently press the toppings into the batter with the back of a spoon.

Bake for 25-30 minutes, until golden brown.

Store in an air-tight container at room temperature.