Chocolate Swiss Roll (Bûche de Noël)

Heat the oven and separate the eggs. Set a rack in the middle of the oven and heat it to 175°C. Line the base of a 43 × 30 cm rimmed tray with baking paper, without oiling the paper. Separate 4 room-temperature eggs, putting the whites in a medium bowl and the yolks in a large one.

Whip the meringue. Add the salt, cream of tartar and 100 g of the sugar to the whites and beat until the sugar has dissolved and the foam stands in glossy stiff peaks, 8–10 minutes.

Make the yolk batter. Beat the remaining 100 g sugar into the yolks for about a minute. Whisk in the cocoa, oil, vanilla and 80 ml water until the cocoa has dissolved. Sieve over the cake flour and baking powder and beat until smooth.

Fold and bake. Stir a quarter of the meringue into the yolk batter to loosen it, then fold in the rest in three additions, stopping while a few streaks remain so the mixture stays billowy. Spread it gently to the edges of the tray and bake until the top springs back when lightly pressed, 18–20 minutes. Leave the cake in the tin for 30–40 minutes.

Whip the filling and roll. Beat the cream with the sugar, instant vanilla pudding, salt and vanilla to medium-firm peaks. Run a spatula around the cake, invert it onto a rack, peel off the paper, then turn it onto a fresh sheet of paper. Spread the cream to the edges and, starting from a short side, roll the cake up with the paper as a guide. Set it seam-side down on a platter and chill at least 30 minutes, or up to 4 hours.

Trim and dust. Trim a thin slice from each end with a serrated knife. Dust the roll with icing sugar just before cutting. The filled cake, undusted, will keep covered in the fridge for 2 days.