Preheat your oven to 350°F (175°C). Line an 8-inch round cake pan with parchment paper and lightly grease the sides.
In a large mixing bowl, whisk together the sifted flour, cocoa powder, baking powder, salt, and sugar until combined and no lumps remain.
Add eggs, vegetable oil, and vanilla to the dry mixture. Mix with a whisk or hand mixer until the batter is smooth and slightly glossy.
Slowly pour in the hot water, a little at a time, while mixing. Continue until the batter is thin, smooth, and well incorporated.
Pour the batter into the prepared cake pan, smoothing the top with a spatula for an even surface.
Bake in the preheated oven for about 40 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Once baked, remove the cake from the oven and let it cool in the pan for 10 minutes. Then, transfer to a cooling rack and cool completely.
Meanwhile, heat the heavy cream in a saucepan over low heat until just simmering. Remove from heat and add the chopped dark chocolate. Let sit for 2-3 minutes, then stir until smooth and glossy to make the ganache.
Pour the ganache over the cooled cake, spreading evenly with an offset spatula or spoon to create a shiny, smooth glaze that drapes beautifully over the sides.
Sprinkle edible glitter or shimmer dust generously over the top of the cake to create a shimmering galaxy effect.
Allow the ganache and glitter to set briefly before slicing. Serve slices showcasing the dark, fudgy interior and shimmering exterior.
