Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch glass baking pan.

Combine brown sugar and butter in a large mixing bowl. Add eggs and vanilla extract, stirring until all is well combined.

Combine flour, baking powder, and salt in a bowl. Add flour mixture to egg mixture, stirring only until incorporated. Fold in candy pieces. Spread batter into the prepared pan; mixture will be thick.

Bake on the center rack of the preheated oven until a toothpick inserted in the center comes out clean, about 25 minutes. Allow to cool 10 minutes before slicing.