Preheat oven to 350°F. Prepare two 9-inch round cake pans by greasing with butter and lining the bottom of the tin with a round of parchment paper.

In a large mixing bowl with a hand mixer, or in the bowl of a stand mixer fitted with the paddle attachment, whisk together the sugar and oil, then mix in the eggs and vanilla. Sift in cocoa powder and whisk just until combined.

In a separate bowl, whisk together the flour, baking soda and salt. With the mixer on low, alternate adding one-third of the flour and one-half of the buttermilk at a time, beginning with the flour, until both are gone.

Microwave the water until very hot, but not quite boiling, then stir in the instant espresso. With the mixer on low, stream in the hot liquid. Mix just until fully combined and scrape the sides and bottom of the bowl with a rubber spatula to ensure everything is homogenous.

Pour the batter into the prepared tin and tap it on the counter to pop any large air bubbles. Bake on the middle rack for 40 minutes or until the tops spring back when lightly pressed and a wooden toothpick comes out clean or with just a few moist crumbs.

Allow the cakes to cool in the tin for 10 minutes then run a knife around the edges of the cakes to loosen them. Turn out the cake onto a wire rack to cool completely.

Make the fudge frosting. In a saucepan, pot or dutch oven at least 2 quarts large, stir together the sugar, cocoa and salt until combined. Add in the heavy whipping cream and corn syrup and cook over medium heat, stirring until the sugar is dissolved and the mixture is smooth, glossy, and just beginning to bubble around the edges. Remove from heat and whisk in the vanilla. Add the butter, two tablespoons at a time, mixing until completely combined. Add the chocolate and whisk until melted, smooth and homogenous.

Transfer to a large mixing bowl (if you have a hand mixer) or the bowl of a stand mixer, cover the surface with plastic wrap and chill for three to four hours or until thick and firm. (To speed this up, stir the mixture a few times while chilling or, alternately, pour the hot fudge over a half sheet tray, cover and chill, then transfer to a large mixing bowl/stand mixer bowl.)

Once the cakes are fully cool, trim off the dome tops with a serrated knife to create a level surface for stacking.

With a hand mixer or in the bowl of a stand mixer with the beater attachment, beat the chilled fudge on medium-high speed until lightened in color and spreadable. It will take a bit to get loosened up — let it sit a minute or two at room temperature if it’s too thick.

Place a small dollop of frosting on your cake plate or board, and center the first cake layer cut side up. Cover the cake top in a thick layer of frosting, all the way to the edges. Gently place the second cake layer on top, cut side down.

Cover the whole cake with a very thin layer of frosting. (This is called the crumb coat as it traps all the crumbs.) Refrigerate for an hour so the cake can firm up, then spread on a top coat using almost all the remaining frosting.

Decorate the cake by piping on designs of any remaining frosting and/or sprinkling on nonpareils. Store in the refrigerator and set out at room temperature one hour before serving.