- 6 tablespoons unsalted butter, cut into pieces
- 2 ounces unsweetened chocolate, chopped
- 4 ounces bittersweet chocolate, chopped
- 1 cup sugar
- 2 large eggs
- 3⁄4 cup all-purpose flour
- 1⁄2 teaspoon salt
- 1 cup walnuts, toasted and chopped coarse
- 3 cups miniature marshmallows
- 1⁄2 cup milk chocolate chips
- 1⁄2 cup semi-sweet chocolate chips
- Preheat oven to 350°F and line a 9-inch square baking pan with nonstick tin foil, crimping to create a 4" 'collar'. Spray with nonstick cooking spray.
- In a heavy 1 1/2-quart saucepan (or microwave on Medium), melt butter, unsweetened chocolate, and bittersweet chocolate, stirring, until smooth and remove pan from heat. Cool mixture 10 minutes.
- Stir in sugar. Add eggs, 1 at a time, beating well with a wooden spoon until mixture is glossy and smooth.
- Mix flour, walnuts and salt separately, then gently stir into chocolate mix.
- Spread batter evenly in pan and bake in middle of oven 20 minutes.
- Remove pan from oven and add chocolate and marshmallows evenly over brownies.
- Bake brownies until marshmallows are puffy and pale golden, 7 to 10 minutes.
- Remove from oven, quickly swirl just the top chocolate/marshmallow with a skewer.
- Cool brownies completely in pan on a rack, then refrigerate until firm.
- Trim edges, then cut into 16 squares with a buttered knife.