Preheat the oven to 350F degrees and line a 9x13 inch pan with parchment so there's an overhang around the sides.
Add the butter and chocolate to a large heatproof bowl. Microwave on medium power for 45-second intervals, stirring between each, until smooth. Do not microwave on high/regular power!
Let the mixture cool slightly, then whisk in the sugar and vanilla extract. Whisk in the eggs 1 at a time.
Gently fold in the cocoa powder, flour and salt.
Pour the mixture into the prepared pan and bake for 30-35 minutes, or until an inserted toothpick comes out clean or with a few damp crumbs.
Cool the brownies fully (keeping them in the pan).
Peanut Butter Layer
In a large bowl, beat the butter until soft.
Beat in the peanut butter.
Beat in the powdered sugar, starting with 2 cups. Slowly beat in the remaining powdered sugar a little at a time until the mixture is thick and the desired sweetness is reached.
Spoon the peanut butter mixture over the brownies. Using a piece of wax paper between your hand and the peanut butter layer, press the mixture down until it's a flat, smooth layer
Place in the fridge for 30 minutes to firm up.
Place the chocolate in a large heatproof bowl.
Heat the cream until almost boiling - either in the microwave or on the stovetop while stirring gently.
Pour the hot cream over the chocolate and let it sit for 3 minutes. Whisk until smooth. If the chocolate isn't quite melted, microwave for 30 seconds on medium power.
Pour the chocolate over the peanut butter layer and spread smooth.
Place in the fridge for the chocolate to set.
Cut into bars.
Instead of making homemade brownies, feel free to use a box mix for a 9x13 inch pan. Prepare the brownies according to the package instructions, then make the remaining layers according to the recipe.I recommend storing these in the fridge in an airtight container so that the peanut butter layer doesn't melt.