Preheat your oven to 350°F. Grease two 8-inch cake pans and dust them with cocoa powder, then line the bottoms with parchment paper to prevent sticking.

In the bowl of an electric mixer fitted with a paddle attachment, combine all the dry ingredients and mix briefly to combine. In a separate medium bowl, whisk together all the wet ingredients, gradually adding the hot water or coffee to avoid cooking the eggs.

Pour the wet ingredients into the bowl with the dry ingredients and mix on medium speed for 2-3 minutes until well combined; the batter will be thin. Divide the batter evenly between the prepared pans, using a kitchen scale if necessary for accuracy.

Bake the cakes for 40-45 minutes or until a cake tester inserted into the center comes out mostly clean. Let cakes cool in the pans for 10 minutes before inverting onto a cooling rack to cool completely.

For the buttercream, combine egg whites and sugar in a stand mixer bowl and whisk until combined. Set the bowl over a double boiler, whisking continuously until the mixture is hot and no longer grainy, approximately 3 minutes.

Return the bowl to the stand mixer and whip the meringue on medium-high speed until stiff peaks form and the bowl is no longer warm, about 5-10 minutes. Change to the paddle attachment, then slowly add the cubed butter and mix until the buttercream is smooth.

Add the cooled melted chocolate to the buttercream and mix until fully incorporated. To assemble the cake, place one layer on a cake stand, spread about 1 cup of buttercream evenly on top, and place the second layer on top.

Apply a thin crumb coat of buttercream around the entire cake and chill for 20 minutes to set. After chilling, spread 1 cup of frosting on top, smoothing the sides and flattening the top, and create a swirl pattern with a large offset spatula.

Using a piping bag with a 1M tip, pipe decorative rows of frosting around the base of the cake, applying even pressure as you rotate the turntable. Work your way up the cake, ensuring the seams align at the back, and finish by decorating the top with chocolate curls, pearls, or sprinkles if desired.