MAKE THE CAKE (NO MIXER REQUIRED):

1. PREP: Preheat the oven to 350 degrees and grease 2 9-inch baking pans (see other size options below) with butter or nonstick cooking spray, line with parchment paper, and then grease the parchment paper. Set aside.
2. MIX DRY INGREDIENTS: Shift the flour, cocoa powder, baking powder, baking soda, and salt into a large bowl. Then add the sugar and whisk to combine.
3. COMBINE WET INGREDIENTS: In another bowl, add the eggs, milk, baking oil, and vanilla extract. Whisk to combine and then slowly add the mixture to the dry ingredients. Mix until combined.
4. ADD HOT WATER/COFFEE: Add the boiling water or hot coffee. Carefully mix together. The batter will be runny. 
5. BAKE: Then add the batter to your prepared pans and bake until a skewer inserted into the center of the cake comes out clean, about 35-40 minutes.
6. COOL: When done baking, let the cake cool for at least 15 minutes before removing them from the cake pans. Let the cakes cool completely on a wire cooling rack before frosting.

FOR THE WHIPPED CHOCOLATE GANACHE FROSTING:

1. PREP THE CHOCOLATE: While the cake is baking, make the chocolate ganache. Start by placing the finely chopped chocolate in a medium heat-proof bowl.
2. HEAT THE CREAM: Next, heat the cream in a small saucepan over medium heat until it begins to simmer gently — not boil. You just want to get it to the point when small bubbles start to form on the edges of the pan.
3. COMBINE INGREDIENTS: Then pour over chocolate and let it sit for 2-3 minutes. Then gently stir with a spoon or spatula until the chocolate is completely melted. (If you’re having trouble getting the chocolate to melt, don’t try to microwave it! See my note below).
4. COOL: Set aside and let cool to room temperature.
5. BEAT: Beat the cooled thickened ganache with a handheld or stand mixer fitted with a whisk attachment on medium-high speed until light in color and has a fluffier texture, about 4 minutes.

FOR THE WHITE CHOCOLATE GANACHE: 

1. HEAT THE CREAM: Again, heat the cream to a simmer. 
2. POUR OVER WHITE CHOCOLATE: Next, pour the cream over the white chocolate pieces and stir until fully melted and combined.
3. COOL: Cool for 30 minutes before using.

ASSEMBLE THE CAKE: 

1. TRIM ANY DOMES: Once the cake is thoroughly cooled, it’s ready to frost! If a dome has formed on the top of your cake layers, carefully slice off the raised section with a serrated knife (so your cake layers are flat).
2. ADD A CRUMB COAT: Then add a super-thin layer of frosting to your cake layers. This is called a crumb coat and is an easy technique used to lock in any loose cake crumbs. Start by adding the frosting to the sides and top of the bottom layer. Then add the second layer and repeat the process. Refrigerate the cake for about 20 minutes before adding the final layer of frosting.
3. ADD THE FROSTING: Next, add the final layer of frosting. I used a metal icing spatula to add the frosting and to smooth out the surfaces. You can also use a bench scraper to get super smooth sides.
4. ADD THE WHITE CHOCOLATE DRIPS & MARSHMALLOWS:  Then add the white chocolate drip layer by adding the white chocolate ganache to a pastry fitted with a medium-size tip (or a plastic bag with one corner snipped off). Drip around the edges of the cake, and then fill in the top. Top with toasted marshmallows.