Decadent Brownies:

* 1 1/4 sticks unsalted butter, plus more, softened, for pan
* 1 cup unsweetened natural cocoa powder
* 1/2 teaspoon fine sea salt
* 1 1/3 cups sugar
* 1 1/4 teaspoon pure vanilla extract
* 2 eggs, at room temperature
* 2/3 cup all-purpose flour
* 1 1/2 cups semisweet chocolate chips

Peanut Butter Buttercream Layer:

* 1 cup creamy peanut butter (don't use old-fashioned or natural)
* 1/2 stick unsalted butter, at room temperature
* 1 cup powdered sugar
* 1/4 teaspoon fine sea salt
* 1 1/4 tablespoons milk
* 1 teaspoon pure vanilla extract
* 1 1/2 cups salted cocktail peanuts

Ganache:

* 2 cups semisweet chocolate chips
* 7 tablespoons unsalted butter