Makes 1 cake (8 inches)
Ingredients :
1½ cups (330 grams) firmly packed light brown sugar
⅔ cup (150 grams) unsalted butter, melted
½ cup (128 grams) creamy peanut butter
3 large eggs (150 grams), room temperature
1½ teaspoons (6 grams) vanilla extract
2¼ cups (281 grams) all-purpose flour
2½ teaspoons (12.5 grams) baking powder
1 teaspoon (3 grams) kosher salt
½ teaspoon (2.5 grams) baking soda
1½ cups (360 grams) whole buttermilk, room temperature
⅔ cup (113 grams) chopped 66% cocoa dark chocolate, melted and slightly cooled
Chocolate Cream Cheese Frosting (recipe follows)

Instructions :
Preheat the oven to 350°F (180°C). Spray 2 (8-inch) round cake pans with cooking spray with flour. Line the bottom of the molds with parchment paper.
In a large bowl, whisk together brown sugar, melted butter, and peanut butter until smooth and creamy. Add eggs and vanilla, whisking until combined.
In a medium bowl, whisk together the flour, baking powder, salt and baking soda. Gradually add the flour mixture to the sugar mixture alternately with the buttermilk, beginning and ending with the flour mixture, whisking just until combined after each addition. Transfer one-third of the dough (about 2 cups [454 grams]) to a medium bowl; Gently stir in melted chocolate until blended. Using 2 tablespoons spring-loaded spoons, alternately spoon peanut butter and chocolate batter into prepared pans. (Each mold will hold approximately 2 cups [approximately 453 grams] of peanut butter dough and approximately 1 cup [approximately 283 grams] of chocolate dough). Using a wooden pick or cake tester, mix the batters together. Gently tap the pans on the counter 2 to 3 times.

Bake until a wooden pick inserted in the center comes out clean, 35 to 40 minutes. Leave to cool in the molds for 10 minutes. Remove from pans and let cool completely on wire racks.
Place 1 cake layer on a cake stand. Spread 1½ cups (about 375 grams) chocolate cream cheese frosting on top. Top with remaining cake layer. Spread remaining frosting over top and sides of cake. Cover and refrigerate until ready to serve.

Chocolate Cream Cheese Frosting:

Ingredients :
2 (8-ounce) packages (454 grams) cream cheese, softened
1 cup (227 grams) unsalted butter, softened
1 teaspoon (4 grams) vanilla extract
½ teaspoon (1.5 grams) kosher salt
4½ cups (540 grams) icing sugar
1 cup (85 grams) dutch cocoa powder

Instructions :
In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese and butter on medium-low speed until smooth and creamy, about 1 minute. Stir in vanilla and salt until blended.
Sift together the icing sugar and cocoa. With the mixer on low speed, slowly add the sugar mixture to the cream cheese mixture, about ¾ cup (90 grams) at a time, beating until combined after each addition and stopping to scrape up the walls of the bowl. Increase mixer speed to medium and beat until light in color and fluffy, about 2 to 3 minutes, stopping to scrape down sides of bowl.