A butterscotch fudge layer and a brownie layer with butterscotch and chocolate chips in the middle makes a very rich treat.
2 cups [304g] unsifted all-purpose flour
1½ teaspoons baking powder
½ teaspoon salt
2 cups [340g] Guittard Real Semisweet Chocolate Chips, divided
2 cups [340g] Guittard Butterscotch Chips, divided
2 tablespoons water, divided
½ cup [113g] unsalted butter
1 cup [215g] firmly packed light brown sugar
3 large eggs
1 teaspoons vanilla extract
¾ cup [90g] coarsely chopped walnuts
Preheat oven to 350ºF. Butter the bottom and line a 9x9-inch pan with foil.
Combine flour, baking powder and salt in a small bowl. Set aside.
Melt 1 cup (6 oz) butterscotch chips with 1 tablespoon water in a small microwave safe bowl at medium power (50% or level 5) for 1-2 minutes, stirring well after 1 minute initially, then at 30 second intervals until smooth. Set aside. If oil separation occurs it will stir back in later.
In another microwave safe bowl melt 1 cup semisweet chocolate chips with 1 tablespoon water following the same procedure used for the butterscotch chips.
Cream butter and brown sugar in large mixer bowl at medium speed until it resembles a ball of dough. Beat in eggs one at a time and vanilla until smooth, stopping to scrape bowl as needed. Add flour mixture on low speed just until incorporated.
Divide the batter into 2 equal parts, adding half to the bowl with the melted butterscotch chips and the other half to the bowl with the melted semisweet chips. Return the contents of the butterscotch bowl and the walnuts to the mixer bowl and mix until evenly combined. Spread into bottom of prepared pan. Sprinkle with remaining 1 cup of semisweet chips and 1 cup butterscotch chips.
Add the melted chocolate and batter to the mixer bowl and mix until combined. Gently layer over chips and spread to edges to cover chips as evenly as possible.
Bake for 40-45 minutes or until the top looks set and dry and springs back when lightly touched. Cool on rack overnight or until cool to touch for about 1-1½ hours, then refrigerate for 1 hour to fully set the chocolate before cutting. Remove foil lined brownie from pan and cut into 16 squares with a large sharp knife.
High altitude adjustments for 7,000 feet:
Reduce baking powder to ¾ teaspoon
Increase flour to 2 ¼ cups
Increase eggs to 3 ½
Reduce bake temperature to 325ºF