1Preheat the oven to 350F. Grease three 6” or 7” cake pans with butter, then dust with flour. Line the bottom with parchment paper rounds. Set aside.
2In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Set aside.
3In a separate large bowl, whisk together the buttermilk, avocado oil, eggs, and vanilla until combined.
4Add the dry ingredients to the wet, and whisk until combined.
5Pour in the hot coffee, and stir quickly until well combined.
6Divide the batter evenly among the three prepared cake pans and bake at 350F for 25-27 minutes, until a toothpick comes out clean.
7Remove the cakes from the oven and set on a wire rack. Allow to cool completely in the pan.
8In a saucepan over medium heat, add the butter, chocolate, and heavy cream.
9Sift in the powdered sugar, cocoa powder, salt, and espresso powder. Mix constantly until the mixture is melted and smooth.
10Once smooth, remove from heat and mix in the vanilla.
11Pour the mixture into a large bowl or baking pan and cover the top with plastic wrap. Allow to cool at room temperature for 30 minutes, then place in the fridge to chill for at least another 1-2 hours.
12If needed and using a serrated knife, slice the tops of each cake layer off to even.
13Place one cake layer cut side up on a cake stand or platter. Spread ~1/4 of the chocolate fudge frosting all over the cake layer, pushing it to the edge. Repeat with the remaining layers.
14After the last cake layer is added on top, with an offset spatula, spread the remaining frosting evenly all over the cake.
15Decorate and garnish with flaky sea salt, as desired.