Preheat oven to 325°. Spray a 15-cup Bundt pan with baking spray with flour.
In a large bowl, beat butter and peanut butter with a mixer at medium speed until creamy, about 1 minute. Add sugars, and beat until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
In another large bowl, whisk together Swans Down® Cake Flour, baking powder, and salt. Gradually add flour mixture to butter mixture alternately with milk, beginning and ending with flour mixture, beating just until combined after each addition.
Remove 1½ cups batter, and place in a medium bowl. Add cocoa, and whisk until combined. Drop one-third of peanut butter batter by heaping tablespoons in prepared pan. Top with alternating heaping tablespoons chocolate batter and remaining peanut butter batter. Using a butter knife, swirl batters together. Tap pan on counter twice to remove air bubbles.
Bake until a wooden pick inserted near center comes out clean, 1 hour to 1 hour and 10 minutes. Let cool in pan for 10 minutes. Remove from pan, and let cool completely on a wire rack. Spoon Peanut Butter Drizzle and Chocolate Drizzle over cooled cake.
Makes 1 cake
Peanut Butter Drizzle
In a large microwave-safe bowl, combine peanut butter, corn syrup, and butter. Microwave on high until butter is softened, 25 to 30 seconds. Stir to combine. Use immediately.
In a large microwave-safe bowl, combine chocolate, corn syrup, and butter. Microwave on high until chocolate is mostly melted, 25 to 30 seconds. Stir until smooth. Use immediately.