Step 1: Prepare the Cake Batter

1. Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.
2. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt.
3. In a separate large bowl, mix the granulated sugar, brown sugar, and vegetable oil until combined.
4. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
5. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, mixing until smooth.

Step 2: Bake the Cake

1. Pour the batter into the prepared cake pan and spread evenly.
2. Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
3. Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Step 3: Make the Peanut Butter Frosting

1. In a large bowl, beat the peanut butter and softened butter together until smooth and creamy.
2. Gradually add the powdered sugar, mixing until well incorporated.
3. Add vanilla extract and a little milk at a time, beating until the frosting reaches a spreadable consistency.

Step 4: Assemble the Cake

1. Once the cake is completely cooled, spread the peanut butter frosting evenly over the top.
2. Optional: Drizzle with melted chocolate or sprinkle crushed peanuts for extra texture.
3. Slice and enjoy!