1. Preheat oven to 350 degrees. Spray a 9-by-13-inch baking pan with cooking spray. Line pan with parchment paper, allowing a 2-inch overhang on the longer sides. Spray the parchment paper with cooking spray. Set the pan aside.

2. Whisk together flour, baking powder, and salt in a medium bowl. In the bowl of an electric mixer fitted with the paddle attachment, mix butter and brown sugar until smooth. Add eggs and vanilla extract, mix until smooth.

3. Slowly add in the flour mixture and mix until just combined. Fold in half of each of the marshmallows, chocolates, butterscotch chips, and caramels.

4. Spread batter into prepared pan. Sprinkle remaining marshmallows, chocolates, butterscotch chips, and caramels on top.

5. Bake until top is golden brown and a cake tester inserted into the center comes out clean, about 35 minutes. Let cool on a wire rack. Lift out of pan, and transfer to a baking sheet. Refrigerate until set, at least 30 minutes.

6. Remove parchment, and cut into about triangles or squares.