Preheat oven to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.,In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.,Add eggs, milk, oil, and vanilla extract. Mix until smooth.,Slowly stir in the hot water or coffee. Batter will be thin.,Divide batter evenly between pans and bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.,Cool cakes in the pans for 10–15 minutes, then turn out onto wire racks to cool completely.,Make the frosting: beat peanut butter and butter until smooth and creamy.,Gradually add powdered sugar, beating until well combined. Add cream or milk as needed to reach spreadable consistency.,Place one cake layer on a serving plate and spread with frosting. Top with second layer and frost the top and sides.,Optional: Garnish with chopped peanuts, chocolate drizzle, or peanut butter cups.