1/2 cup butter
1 cup butterscotch chips
2/3 cup packed brown sugar
1 teaspoon vanilla extract
1 1/2 cups flour
2 teaspoons baking powder
1/2 teaspoon salt
2 cups miniature marshmallows
1 cup semi-sweet chocolate chips
Preheat oven to 350 degrees F.
Lightly spray a 13x9-inch baking pan with no-stick cooking spray; set aside.
In a microwave-safe bowl (or in a small saucepan over low heat), melt the butterscotch chips and butter together, stirring occasionally until smooth; set aside to cool.
In a large bowl, stir together the brown sugar, eggs, and vanilla.
Mix in the melted butterscotch chips.
Stir in the flour, baking powder and salt until smooth.
Stir in the marshmallows and chocolate chips.
Spread the batter evenly into the prepared baking pan.
Bake for 15 to 20 minutes in preheated oven.
Cool, then cut into squares.