Preheat the oven to 350F
In a large bowl, whisk together flour, sugar, cocoa, baking soda, baking powder, and salt.
In a separate large bowl, beat eggs, oil, buttermilk, and vanilla for 1 minute.
Sift the dry ingredients into the wet ingredients and stir until combined. Pour in the hot water and mix. The batter will be liquidy.
Grease your 13 x 9 pan generously with coconut oil, and pour in the batter.
Bake for 25 - 30 minutes, or until a knife or tester poked through the center of the cake comes out clean.
Allow the cake to cool completely. (If you’re in a hurry, pop the cake in the freezer. It will cool in about 10-15 minutes)
When cooled, run a spatula gently along the edge of the pan and turn upside down onto a clean surface to remove the cake. Using your circular cutter, cut out 12 cakes from the sheet. (There will be leftover cake-- yay! If you have two 12 cup muffin tins, you are welcome to double the marshmallow and make 24 tails.)
While the cake cools, reduce oven heat to 325F. Spread the coconut flakes out evenly on a rimmed baking sheet and bake for 5-10 minutes, stirring 2-3 times throughout cooking.
Grease the muffin tin with coconut oil.
Cut 2 pieces of plastic wrap 1 and a half times the length of the muffin tin.
Center the first sheet over 2 rows of the muffin tin. Starting from the inner cups, use your fingers to fit the plastic wrap snuggly into each cup. Be sure that the wrap covers the entire inside of the cup.
Center the second piece over the third row and repeat.
Then, grease each cup generously with coconut oil. (This will make it absolutely certain that the marshmallow will pop out of the mold with ease. The oil will also help the coconut to stick to the surface of the marshmallow!)
In a small saucepan, combine the gelatin and the cold water. Stir a few times so that all of the gelatin powder is moistened, and let sit 5 minutes.
Turn on the heat to medium-low, add the sugar, and stir to combine. Continue to cook without boiling, stirring occasionally, until the mixture is no longer cloudy.
When clear, transfer the gelatin mixture to a large mixing bowl. Add the corn syrup and whip on high speed until thickened, fluffy, white, and tripled in volume. (This will take quite a while!)
Working quickly before the marshmallow cools, transfer the marshmallow to a piping bag with a 1 inch opening (no tip) and fill the muffin cups nearly to the top. Immediately press one of the circular cut cakes into each cup so that the sides of the cakes are coated.
Allow to rest for 1 hour.
One by one, use the plastic wrap to pull each cake out of the tin. Roll the outer marshmallow layer in toasted coconut, and serve! Cakes can be stored in an airtight container for up to 3 days.