For Chocolate Cake ::
Preheat oven to 350. Line two 9-inch cake pans with non-stick spray and line the bottoms with parchment paper.
In a large bowl, whisk together sugar, flour, cocoa powder, baking soda, baking powder, and salt. Whisk in eggs, milk, vegetable oil, vanilla and simmering water. The batter will be very thin, don’t worry.
Divide batter into two cake pans, place on middle rack of oven and bake for 15 minutes. Rotate the pans half way through, and bake an additional 10-15 minutes, or until a toothpick inserted into the middle comes out clean.
Remove from oven and let rest in pans on a wire rack for 10 minutes. Turn out onto wire rack to finish cooling.

For Marshmallow Filling:
Sprinkle gelatin over the cold water and allow to sit for five minutes so the gelatin activates and “blooms”. Microwave for 30 seconds until the gelatin dissolves. In a large bowl, mix together gelatin, butter, vanilla and salt. Let rest until just warm. Whisk in marshmallow until the mixture is smooth. Place in the fridge to set for about 30 minutes.

To assemble ::
Cut one of the two rounds of cake into 8 even wedges. Line a medium round mixing bowl with plastic wrap, allowing the edges to meet in the middle. Press the edges all together so the cake is secure in the bowl. Fill with 1 to 1 ¼ cups of marshmallow mixture. Place the other round of cake on top and press down to secure the cakes together. Cover and place in fridge for one hour to set.

Invert the set cake onto a cake plate or dish and remove the bowl and plastic wrap. Cover cake with the remaining marshmallow frosting. Sprinkle with coconut, and gently press into the marshmallow to ensure it sticks.

Slice immediately and serve or lightly cover and chill until ready.