Ingredients:

• 10 tablespoons unsalted butter
• 1 1/4 cups granulated sugar
• 3/4 cup plus 2 tablespoons (80 grams) unsweetened cocoa powder, natural or Dutch-process
• 1/4 teaspoon sea salt
• 1 teaspoon vanilla extract
• 2 large cold eggs
• 1/2 cup all-purpose flour
• 1/2 cup peanut butter

Method:

Preheat oven to 325 degrees F. Line the bottom and sides of an 8-inch square baking pan with parchment paper or aluminum foil, leaving an overhang on two opposite sides.

Set up a double boiler with barely simmering water. Combine butter, sugar, cocoa powder, and salt in the double boiler. Stir mixture occasionally until the butter has melted and mixture is quite warm and looks a bit like chocolate.

Remove the bowl from heat and set aside for 3 to 5 minutes to cool slightly. Stir in vanilla with a spatula. Then, add eggs, one at a time, stirring vigorously after each one. When the batter looks shiny and well blended, add a tablespoon of flour at a time, stirring until fully incorporated between additions, then vigorously beat with a spatula for an additional 50 strokes.

Pour batter into prepared pan, then drop spoonfuls of peanut butter into the batter. With a knife, swirl the peanut butter into the batter.