BROWNIES

3/4 cup (1 1/2 sticks) unsalted butter
7 ounces bittersweet or semisweet chocolate, chopped
3 ounces unsweetened chocolate, chopped
1 1/2 cups sugar
1 1/2 teaspoons vanilla extract
1/4 teaspoon salt
4 large eggs
1 cup all purpose flour
1 cup roasted salted peanuts, coarsely chopped

FROSTING AND GANACHE

1 cup chunky peanut butter (do not use natural or old-fashioned)
1/2 cup (1 stick) unsalted butter, divided, room temperature
3/4 cup powdered sugar
1/8 teaspoon salt
1/8 teaspoon ground nutmeg
1 tablespoon whole milk
1 teaspoon vanilla extract

7 ounces bittersweet or semisweet chocolate, chopped