The construction of a classical French layer cake (gâteau) from a baked génoise sponge (Entry 20) — sliced into even horizontal layers, soaked with a flavoured syrup, spread with buttercream or crème mousseline, reassembled, and coated. The génoise assembly is not a single technique but the management of four variables: the evenness of the sponge layer slices, the quantity and flavour of the soaking syrup, the correct temperature of the buttercream for spreading, and the straightness of the finished coating. Each variable, uncontrolled, produces a visually imperfect result.
**The horizontal cut:** - Génoise sliced into layers with a serrated knife, using toothpicks as guides at the correct height (2.5cm per layer) around the circumference — the knife guided by the toothpicks at each cut for perfectly horizontal slices. - Minimum 3 layers for an impressive height; 5 layers for a celebration gâteau. **Soaking syrup:** - The génoise's egg-foam structure produces a relatively dry sponge — the soaking syrup is not optional decoration but a textural requirement. Each layer receives enough syrup to saturate its surface to the correct depth without becoming wet. - Flavour: matched to the filling — Grand Marnier for a chocolate-orange gâteau, Kirsch for a black forest, rum for a tropical construction. **Buttercream temperature:** - Italian meringue buttercream must be at approximately 18–20°C for spreading — cool enough to hold its shape, warm enough to spread smoothly. Too cold: it tears the sponge surface. Too warm: it flows off and does not hold even layers. **The crumb coat:** - A thin first coat of buttercream applied over the entire assembled cake and refrigerated for 15 minutes — this traps any sponge crumbs and provides a clean foundation for the final coat. - Second coat applied after refrigeration: the final, smooth surface from which all decoration proceeds. Decisive moment: The crumb coat refrigeration stage. Applying a final decorative coat directly over loose sponge crumbs produces a crumb-contaminated surface. The crumb coat traps every loose crumb; the refrigeration sets it as a physical barrier. This step takes 15 minutes and saves the entire appearance of the finished cake.
Jacques Pépin's Complete Techniques