Preparation:

Step 1: Prepare the Chocolate Cake

1. Preheat your oven to 350°F (177°C). Grease and line three 8-inch round cake pans with parchment paper.
2. In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt until well combined.
3. Add the eggs, oil, sour cream, buttermilk, and vanilla extract. Beat the mixture on medium speed until smooth.
4. Gradually add the hot water or coffee while mixing. The batter will be thin—this is normal and ensures a moist cake.
5. Divide the batter evenly among the prepared cake pans.
6. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean.
7. Allow the cakes to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

Step 2: Prepare the Peanut Butter Frosting

1. In a large bowl, beat the softened butter and peanut butter together on medium speed until creamy and smooth.
2. Add the confectioners’ sugar, vanilla extract, and a pinch of salt. Mix on low speed until combined.
3. Increase the speed to medium-high and add the heavy cream. Beat until the frosting is light, fluffy, and spreadable.

Step 3: Assemble the Cake

1. Place the first cake layer on a serving plate or cake stand. Spread a generous layer of peanut butter frosting on top.
2. Sprinkle a handful of chopped mini peanut butter cups over the frosting for added texture.
3. Repeat the process with the second cake layer.
4. Place the third cake layer on top and apply a thin crumb coat of frosting to the entire cake to seal in crumbs. Refrigerate the cake for 30 minutes to set the crumb coat.

Step 4: Prepare the Chocolate Ganache

1. Place the chopped chocolate in a heatproof bowl.
2. Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer. Do not let it boil.
3. Pour the hot cream over the chopped chocolate and let it sit for 2–3 minutes.
4. Stir until the ganache is smooth and glossy. Allow it to cool slightly until it reaches a pourable consistency.

Step 5: Decorate the Cake

1. Divide any remaining peanut butter frosting into several bowls and tint each with food coloring gels to create vibrant galaxy colors (e.g., blue, purple, and pink).
2. Using a spatula, apply dollops of each colored frosting onto the crumb-coated cake. Gently swirl the colors together to create a galaxy effect.
3. Pour the slightly cooled ganache over the top of the cake, letting it drip down the sides for a dramatic effect.
4. Sprinkle edible glitter or stars over the ganache for a cosmic sparkle.
5. Finish by decorating the top with additional mini peanut butter cups and other chocolate pieces.