For the Cake: Adjust oven rack to lower-middle position and preheat to 350°F (180°C). Lightly grease one 9- by 4-inch aluminum Pullman loaf pan with neutral oil and line with parchment cross-wise so that there is a 1-inch overhang on both sides. (See notes below if you do not have a Pullman loaf pan.)

In a large bowl, whisk eggs, oil, sugar, salt, and coffee to combine. Using a fine-mesh sieve, sift flour, cocoa powder, baking soda, and baking powder into egg mixture. Whisk until combined. Whisk in the crème fraîche until smooth and no streaks remain. Using a flexible spatula, scrape mixture into the prepared pan.

Bake until the cake is just set and a skewer inserted into the center of the cake comes out clean, 50 to 60 minutes. The cake will feel just barely set and very tender. Let cool in the pan for 20 minutes, then run an offset spatula or butter knife around the edges to loosen. Gently lift parchment to remove cake from pan, then transfer to a wire rack. Pull parchment to remove and allow cake to cool completely, about 1 hour.

For the Frosting: In a small bowl, whisk 1 teaspoon powdered gelatin with 1 ½ tablespoons water. Let sit until gelatin has bloomed, about 3 minutes.

In a medium saucepan, whisk cornstarch, granulated sugar, and salt to combine. Add water, bring to a simmer over medium-low heat, and cook until mixture just begins to thicken and gel, about 2 minutes. Remove from heat, then whisk in gelatin and chocolate, stirring constantly until gelatin and chocolate have melted and mixture is smooth, 1 minute.

Using a fine-mesh sieve, strain chocolate mixture into a medium bowl. Press plastic wrap against surface and let cool slightly, about 5 minutes. (It should be warm and pourable, but should no longer be steaming hot.)

To Assemble: Set cake on cutting board and, using a serrated knife, carefully remove top of cake to level it; set scraps aside for snacking or another use. Slice cake into 2 even layers. Place bottom of the cake back onto the wire rack set inside the rimmed baking sheet and top with ⅓ of the frosting, using an offset spatula to spread it evenly from edge to edge. Top with second layer of cake. Using an offset spatula, spread remaining frosting over the top and sides of the cake, letting excess drip off beneath onto wire rack.

Let cake sit on wire rack until frosting is set and does not leave any trace on your fingertips, about 30 minutes. Using a sharp chef’s knife, slice cake and serve. (For cleaner cuts, run knife under warm water and dry knife with a clean kitchen towel before portioning each slice.)