Start by preparing the ganache. Chop chocolate into small chunks and set aside. Whisk coconut milk, sweetener, and salt together in a saucepan and heat over medium heat until the mixture starts to release steam but does not come to a boil, about 3-5 minutes. Remove from heat and whisk in vanilla extract. Add chopped chocolate and let it sit for 10-20 seconds so that it starts melting. Then whisk the chocolate into the coconut milk until the mixture is glossy and smooth, about 30 seconds.
Transfer ganache to the bowl of a stand mixer or a mixing bowl if you will be using a hand mixer. Place a piece of plastic wrap directly onto the ganache and refrigerate for at least 2 hours or overnight until the ganache is firm and set.
Bake the cake while the ganache chills. Preheat oven to 350˚F or 180˚C with rack in the center. Cut an 8” diameter circle out of parchment paper (trace the bottom of an 8” round cake pan onto the paper before you grease the pan or use these pre-cut parchment circles). Grease an 8” round cake pan then press the parchment paper round into the bottom of the pan. Grease the top of the parchment paper then dust the interior bottom and sides with flour or sifted cocoa powder, tapping out excess. Sift flour, sugar, cocoa powder, baking soda, and salt into a mixing bowl, then whisk to evenly combine.
Whisk together hot coffee or water, oil, vinegar, and vanilla extract in a separate bowl or large measuring cup.
Add wet mixture to dry mixture and whisk to combine for about 30 seconds until you have a smooth, runny batter. Be careful not to over-mix the batter, and don't whisk vigorously.
Pour batter into the prepared cake pan and bake at 350˚F for 35-40 minutes, until the cake comes away from the sides of the pan and a toothpick inserted into the center of the cake comes out clean. Remove from oven.
Cool cake in pan for 5 minutes then invert the cake pan onto a cooling rack and lift the cake pan off from the cake. The pan should release easily. Peel the parchment paper off of the cake and let the cake cool to room temperature before frosting it.
When the ganache has set in the fridge, take it out and whip it with a balloon whisk attachment on a stand mixer or with a hand mixer on high speed until it is smooth, shiny, and fluffy, about 2-3 minutes.
Transfer the cooled cake to a serving dish or cake plate with the top of the cake facing up. Spread the whipped ganache in one thick layer over the top of the cake using an offset spatula.
Cut cake into slices and serve.