- 2 1/4 cups all-purpose flour
- 2 1/4 teaspoons baking powder
- 1 teaspoon salt
- 1 stick (4 ounces) unsalted butter, at room temperature
- 1 1/2 cups packed dark brown sugar
- 3 large eggs
- 1 teaspoon vanilla extract
- 1 cup miniature marshmallows, divided
- 1 cup semisweet chocolate chips, divided
- 1 cup white chocolate chips, divided
- 1 cup butterscotch chips, divided
- 18 soft caramel candy cubes, coarsely chopped, divided
Preheat the oven to 350°F. Spray a 9x13-inch baking pan with nonstick cooking spray. Line pan with parchment or foil, leaving an overhang on the longer sides of the pan. Spray parchment with nonstick cooking spray.
In a medium bowl whisk together the flour, baking powder, and salt.
In a large bowl, use an electric mixer to beat the butter and brown sugar on medium speed until well combined. Add the eggs and vanilla, beating to combine. On low speed gradually add the flour mixture until incorporated. Fold in 1/2 cup each of the marshmallows, semisweet chocolate chips, white chocolate chips, butterscotch chips, and half the caramels.
Spread the batter evenly into the prepared pan. Sprinkle with the remaining marshmallows, semisweet chocolate chips, white chocolate chips, butterscotch chips, and caramels. Bake until the top is golden brown, about 35 minutes. Let cool on a wire rack. Use parchment to lift out of pan. Cut into 32 squares and serve. Bars can be stored in airtight containers at room temperature for 1 week.