Preheat your oven to 350°F (175°C). Prepare two 9-inch round cake pans with cooking spray or parchment paper.

In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt until combined.

Add the eggs, milk, oil, and vanilla to the dry ingredients. Mix until just combined.

Carefully stir in the boiling water.

Divide the batter evenly between the prepared pans. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Let it cool in the pans for about 10 minutes, then turn out onto wire racks to cool completely.

In a medium mixing bowl, beat the softened butter until creamy. Slowly add the peanut butter and mix until smooth.

Gradually add in the powdered sugar. Mix until combined, adding milk as necessary to achieve a light and fluffy frosting.

Once the cakes are cool, place one layer on a serving plate. Spread a generous amount of peanut butter frosting on top. Add the second layer and frost the top and sides of the cake.

For the galaxy glaze, heat the heavy cream until just simmering. Pour it over the chopped dark chocolate and white chocolate. Let it sit for a few minutes, then stir until smooth.

Pour the glaze over the frosted cake, encouraging it to drip down the sides. Top with a sprinkle of edible glitter.