I preheat the oven to 350°F (175°C) and grease a 9x13-inch baking pan, lining it with parchment paper for easy removal.

In a medium bowl, I sift 2 cups flour, ¾ cup cocoa powder, 1 tsp baking powder, 1 tsp baking soda, and ½ tsp salt. I set this aside for the base of Chocolate Peanut Butter Cake.

In a large bowl, I whisk 1 ½ cups granulated sugar, 2 eggs, 1 cup milk, ½ cup vegetable oil, and 2 tsp vanilla extract until smooth.

I gradually fold the dry ingredients into the wet, mixing until just combined to avoid a dense cake. I slowly pour in 1 cup boiling water, stirring gently—the batter will be thin. I fold in ½ cup sour cream for richness and stability.

I pour the batter into the prepared pan and bake for 35–40 minutes, until a toothpick inserted in the center comes out clean. I cool the cake in the pan for 10 minutes, then transfer to a wire rack to cool completely.

In a small saucepan, I melt 1 cup chocolate chips, ½ cup heavy cream, 2 tbsp butter, and 1 tsp vanilla extract over low heat, stirring until smooth. I let it cool slightly until spreadable.

I beat ½ cup softened butter and 1 cup creamy peanut butter until fluffy. I gradually add 2 cups powdered sugar, ¼ cup heavy cream, 1 tsp vanilla extract, and a pinch of salt, beating until smooth and spreadable.

If using the fudge filling, I spread it evenly over the cooled cake and let it set for 15 minutes. I then spread the peanut butter frosting over the top, creating soft swirls with a spatula.

I slice and serve the cake at room temperature, savoring its rich, creamy flavors with a hot drink or dessert board.