Preheat oven to 325°F (165°C). Grease and line the bottoms of three 8-inch round cake pans with parchment.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a stand mixer fitted with the whisk attachment, beat the eggs and sugar on medium-high speed for 2–3 minutes, until pale and thickened.

With the mixer on low, slowly stream in the oil, mixing until fully incorporated. Then, add the buttermilk and vanilla, mixing to combine.

Add the dry ingredients to the wet mixture and whisk by hand until no streaks of flour remain. Divide the batter evenly among the prepared pans. Tap each pan gently on the counter to release surface bubbles.

Bake for 25–30 minutes, or until springy in the center and a toothpick inserted comes out clean.

Let the cakes cool in their pans for 10–15 minutes, then run an offset spatula around the edges to loosen. Flip each cake firmly onto a wire rack, remove the parchment, and let cool completely.

Once fully cool, use a serrated knife to split each cake horizontally to create 6 total layers.

While the coffee is still hot, whisk in the sugar until fully dissolved. Then, stir in the coffee liqueur, vodka, vanilla, and salt. Let cool to room temperature before using.

In a stand mixer fitted with the whisk attachment, combine the egg yolks, sugar, salt, and cornstarch. Whip on high speed for 4–5 minutes, until thick, pale, and ribboning.

Add the cold mascarpone and beat on medium-high speed until completely smooth and lump-free, scraping down the bowl as needed.

Add the vanilla and cold heavy cream, and whip on medium-high until the mixture reaches firm peaks, about 2–3 minutes. Reserve about 1 ¼ cups of the finished cream.

Place an 8-inch cake ring or springform pan on a cake stand or serving plate that fits in your fridge. Line the inside with a tall strip of acetate.

Place one cake layer inside the ring, cut side up. Brush generously with the espresso soak. Add a layer of mascarpone cream and smooth with the back of a spoon or an offset spatula.

Repeat with the remaining layers, finishing with a final layer of cake, cut side up, then brush generously with espresso soak. Chill the assembled cake in the refrigerator for at least 8 hours, preferably overnight.

Just before serving, remove the cake ring, leaving the acetate in place. Pour the reserved, thinned mascarpone cream onto the top layer, allowing it to fill the top and settle within the acetate collar.

Dust the top generously with Dutch-process cocoa powder. Serve cold. Store the cake in the refrigerator for up to 3 days.