• Preheat the oven to 350°F and line an 8x8-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
• Melt the butter in a medium saucepan over medium-low heat. Once fully melted, remove it from the heat and immediately stir in the sugar. Let the mixture cool for 5–10 minutes, until it is warm but not hot to the touch.
• Whisk in the eggs, one at a time, whisking for at least 1 minute after each addition. Then stir in the salt and vanilla.
• Sift in the cocoa powder, baking powder, and flour, then stir until a glossy chocolate batter forms. Pour the batter into the prepared pan.
• Spread the batter evenly in the pan, making sure it reaches the corners, then smooth the top. Let the batter rest for 10 minutes.
• Bake for 30 minutes, or until the edges look dry and the center is still slightly underbaked. A toothpick inserted into the center should come out with a little moist batter.
• Cool the brownies completely before adding the peanut butter layer.

Peanut Butter Layer

• Beat the butter and peanut butter together until smooth. Mix in the powdered sugar, vanilla, and salt. The mixture will look crumbly. Press it evenly over the cooled brownies.

Chocolate Topping

• Add the butter and chocolate to a microwave-safe bowl. Microwave for 30 seconds, then stir. Continue microwaving in 15-second intervals, stirring after each interval, until the mixture is smooth and fully melted. Let it cool for 5 minutes.
• Pour the chocolate mixture over the peanut butter layer and spread it evenly. Chill for 30–60 minutes before slicing.