Step 1: Prepare the Cake Batter

1. Preheat the oven to 350°F (175°C). Grease and line three 8-inch cake pans with parchment paper.
2. In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
3. In a separate bowl, whisk sugar, vegetable oil, eggs, and vanilla extract until well combined.
4. Gradually add the dry ingredients to the wet ingredients, alternating with buttermilk and hot coffee, mixing until smooth.

Step 2: Bake the Cakes

1. Divide the batter evenly among the prepared pans.
2. Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
3. Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Step 3: Make the Buttercream Frosting

1. Beat butter on high speed for 3–4 minutes, until light and creamy.
2. Gradually add powdered sugar, mixing on low.
3. Add heavy cream and vanilla extract, then increase the speed to high and beat until fluffy.
4. Divide the frosting into separate bowls and tint each portion with blue, black, purple, and pink food coloring.

Step 4: Assemble and Decorate

1. Place one cake layer on a stand and spread a thin layer of frosting. Repeat with the remaining layers.
2. Apply a crumb coat (thin frosting layer) and chill the cake for 20 minutes.
3. Using an offset spatula, apply the different colored frostings in random patches, then blend them to create a galaxy effect.
4. Add edible glitter, silver sprinkles, or white food coloring splatters to mimic stars.