Preheat oven to 350°F (175°C). Grease and line the bottom of two 8-inch round cake pans (or one 9x13 pan) with parchment paper and lightly grease the sides.

Dry ingredients

In a large bowl, sift or whisk together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, baking soda, and 1 teaspoon fine salt until evenly combined.

Wet ingredients

In a separate medium bowl, whisk the eggs, whole milk, neutral oil, and vanilla extract until smooth.

Combine batter

With the mixer on low, add the wet mixture to the dry ingredients and mix until incorporated. Gradually pour in the hot brewed coffee while mixing slowly—the batter will be thin. Scrape the bowl and mix just until uniform.

Bake

Divide batter evenly between prepared pans (or pour into 9x13 pan). Bake for 25–30 minutes for 8-inch pans or 30–35 minutes for a 9x13, until a toothpick inserted near the center comes out with a few moist crumbs. Do not overbake to keep the cake fudgy.

Cool

Allow cakes to cool in pans on a wire rack for 10–15 minutes. Run a knife around edges, invert onto racks, remove parchment, then cool completely before adding fudge layer and ganache.

Fudge Layer (optional but recommended)

Prepare fudge

Place semisweet chocolate chips in a heatproof bowl. In a small saucepan, warm 1/2 cup heavy cream, 2 tablespoons unsalted butter, 1 tablespoon light corn syrup, and 1/8 teaspoon fine salt until it just begins to simmer. Pour the hot cream mixture over the chocolate and let sit for 1 minute, then whisk until smooth and glossy.

Apply fudge layer

If using two cake layers, place the first layer on a cake board or serving plate. While fudge is warm but slightly cooled (pourable), spread about half over the top of the first layer to form a dense fudgy filling. Place the second cake layer on top. If using a 9x13 pan, spread fudge evenly over the cooled cake surface. Chill for 15–20 minutes to set slightly before glazing.

Chocolate Ganache (glaze)

Make ganache

Place chopped dark or semisweet chocolate in a bowl. Heat 3/4 cup heavy cream in a small saucepan until it just begins to simmer (do not boil). Pour the hot cream over the chocolate and let sit 1 minute. Add 1 tablespoon butter if using. Stir gently until smooth and glossy and fully combined.

Glaze the cake

Let ganache cool 3–5 minutes until slightly thickened but still pourable. Place the cake on a wire rack set over a sheet pan to catch drips. Pour ganache over the center of the cake and use an offset spatula to gently coax it to the edges, allowing it to drip down the sides. If you used a fudge layer between two layers, pour ganache over the top and let excess drip down the sides. For a 9x13, pour and spread evenly.

Set

Let the glazed cake sit at room temperature for 30–45 minutes to allow the ganache to set to a glossy finish. For a firmer set, refrigerate for 20 minutes, then bring back to room temperature before serving for optimal texture.

Finishing

Decorate

Once ganache is set, dust the top lightly with 1 tablespoon unsweetened cocoa powder using a fine sieve if desired. Sprinkle sea salt flakes (about 1/4 teaspoon total) sparingly over the top to enhance chocolate flavor.

Slice and serve

Use a warm, clean knife (dip in hot water and wipe dry between cuts) to slice neat pieces. Serve at room temperature or slightly warmed with a scoop of vanilla ice cream or whipped cream.