Center an oven rack and preheat the oven to 350°F (175°C). Grease and line an 8-inch or 9-inch round cake pan with parchment paper; grease the paper as well. If you prefer a layered cake, use two 8-inch pans and divide batter evenly.

Dry ingredients

In a medium bowl whisk together 1.5 cups all-purpose flour, 0.5 cup unsweetened cocoa powder, 1 tsp baking powder, 0.5 tsp baking soda, and 0.5 tsp fine sea salt until evenly combined and aerated. Set aside.

Wet ingredients

In a large mixing bowl whisk together 1.25 cups granulated sugar and the 3 large eggs until pale and slightly thickened, about 1–2 minutes by hand or 30–45 seconds with a mixer on medium speed. Add 0.75 cup melted, slightly cooled unsalted butter, 0.75 cup whole milk (or buttermilk), and 2 tsp vanilla extract; whisk until smooth.

Combine and finish batter

Add the dry ingredients to the wet ingredients in two additions, folding gently until just combined. Do not overmix. Stir in 1/2 cup hot brewed coffee or hot water a little at a time — the batter will loosen and become smoother. Pour the batter into the prepared pan(s) and smooth the top with a spatula. Tap the pan on the counter once to release big air bubbles.

Bake

Bake in the preheated 350°F (175°C) oven: for a single 9-inch pan bake 28–34 minutes, for single 8-inch pan bake 30–36 minutes, or for two 8-inch pans bake 22–26 minutes. Cake is done when a toothpick inserted into the center comes out with a few moist crumbs (not wet batter) and the top springs back lightly when touched.

Cool

Remove cake from oven and let rest in the pan on a wire rack for 10–15 minutes. Run a knife around the edges, invert onto the rack to remove from the pan, then invert again if desired so the top faces up. Cool completely (about 1–2 hours) before frosting to prevent melting the ganache.

Cloud Whipped Ganache Frosting

Warm the cream

Place 1 cup heavy cream in a small saucepan and heat over medium until it just begins to simmer and small bubbles form at the edge — do not boil. Alternatively microwave in 30-second bursts until steaming.

Make ganache

Place 10 oz chopped dark chocolate in a heatproof bowl. Pour the hot cream over the chocolate and let sit undisturbed for 2–3 minutes to melt. Add 2 tbsp room-temperature unsalted butter, 0.5 tsp vanilla extract, and 1/8 tsp fine sea salt. Gently stir from the center outward with a spatula until smooth and glossy. If any unmelted pieces remain, microwave the bowl in 10-second bursts, stirring between bursts, until fully smooth.

Chill and whip to cloud texture

Cover the ganache with plastic wrap pressed to the surface and chill in the refrigerator for 45–60 minutes, or until the ganache has thickened to a pipeable but still soft consistency (it should be cool and slightly firm but not solid). Optionally, for a lighter 'cloud' texture, transfer chilled ganache to a mixing bowl and whip with a hand mixer on medium-high for 1–2 minutes until it becomes paler, holds soft peaks, and feels fluffy. If you added confectioners' sugar (2 tbsp) for stability, add it before whipping.

Frost the cake

Place the cooled cake layer(s) on a serving plate or turntable. If layering, put a dollop of whipped ganache between layers and spread evenly. Use an offset spatula to spread ganache over the top and sides in a light, cloud-like texture — use gentle, small swirling motions to create soft peaks and valleys. Chill the frosted cake for 15–30 minutes to set slightly before serving, if desired.

Optional Garnish

Dust the top lightly with 1 tsp cocoa powder using a fine sieve. Scatter 1/4 cup chocolate shavings or curls over the top and along the edges. Finish with a pinch (about 1/4 tsp) of sea salt flakes if you like a salted contrast. Return to the refrigerator for 10 minutes if the garnishes need to set, then bring to room temperature 20–30 minutes before serving for the best texture and flavor.