Prep the pan and oven. Heat oven to 350°F (175°C). Line a 10x15-inch jelly roll pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.

Mix dry ingredients. In a large bowl, whisk flour, sugar, cocoa, baking powder, baking soda, and salt until no streaks remain.

Add wet ingredients (except hot liquid). Whisk in milk, oil, egg, and vanilla until smooth and glossy. Don’t overmix—just blend to a uniform batter.

Finish with hot coffee or water. Pour in the hot liquid and whisk gently. The batter will be thin—this is ideal for a tender, moist crumb.

Spread and bake. Pour batter into the prepared pan. Tilt and spread to reach the corners in an even layer. Bake 12–15 minutes, or until the top springs back and a toothpick comes out clean.

Cool completely. Set the pan on a rack for 10 minutes, then lift the cake out using the parchment. Cool fully before cutting. Slightly chilled cake cuts cleanest, so you can refrigerate it for 20 minutes.

Make the frosting. Beat butter until creamy and pale. Add powdered sugar, cocoa, vanilla, and salt. Beat on low to combine, then add cream 1 tablespoon at a time until smooth and spreadable. Whip on medium for 1–2 minutes for a light, silky texture.

Punch out rounds. Use the round cutter to press straight down through the cake. Twist gently to release. Aim for an even number of rounds—each dessert has two or three layers.

Assemble layers. Pipe or spread a thin layer of frosting on one round. Top with another round and repeat if making a triple stack. Finish with a neat swirl of frosting on top.

Add garnish. Sprinkle a tiny pinch of flaky sea salt, add chocolate curls, or place a fresh raspberry on top. Keep it minimal for a clean look.

Chill to set. Refrigerate assembled rounds for 20–30 minutes to firm up before serving. This helps the layers hold when sliced or plated.