6 oz. semi-sweet baking chocolate or dark chocolate, coarsely chopped (such as Baker's brand semi-sweet chocolate—I use a 72% Pound Plus Bar from Trader Joe’s)
3/4 cup unsalted butter
1 1/2 cups granulated sugar
1/2 cup light brown sugar, packed
2 tbsp. espresso or brewed coffee, any temperature; optional but recommended
1 1/2 tsp. vanilla extract
3 large eggs
1 cup all-purpose flour
Pinch of salt to taste, optional

For the peanut butter buttercream:
1 cup creamy peanut butter (I recommend Jif or Skippy—not a fancy, high-end or natural peanut butter, since they separate, and your frosting results could be compromised)
1/2 cup unsalted butter, softened
2 tsp. vanilla extract
1 1/2 to 2 cups confectioner's sugar
Pinch of salt to taste, optional
Sprinkles, optional