Black Sesame and Yuzu Vertical Layer Cake

STEP 1: MAKE THE LIME AND YUZU CURD

Whisk the egg yolks, caster sugar and cornflour together until pale and completely smooth, with no dry pockets of cornflour. Combine the yuzu juice, lime juice, lime zest and salt in a small heavy-based saucepan and bring to a bare simmer, then pour it onto the yolks in a thin stream, whisking constantly. The cornflour is the correction here: a classic butter-set curd flows, and a filling that flows cannot hold a standing spiral up.

STEP 2: COOK OUT THE CORNFLOUR AND CHILL

Return everything to the pan over medium-low heat and whisk without pause until it thickens and reaches a bubble at 92-95C, then hold it there for a full minute so the starch cooks out - stop short of this and the curd tastes floury and slackens as it stands. It will look alarmingly thick, which is correct. Off the heat, beat in the cold butter a cube at a time, push the curd through a fine sieve, press cling film onto its surface and refrigerate at least two hours until fridge-cold and firm.

STEP 3: TOAST AND GRIND THE BLACK SESAME

Heat the oven to 190C / 170C fan / 375F and line the baking sheet with parchment, leaving an overhang on the long sides. Toast the black sesame seeds in a dry pan over medium heat for two to three minutes until they smell nutty, then grind them finely. Grinding matters: whole seeds give speckle and little flavour, while ground seeds give both the slate-grey crumb and the savoury depth the judges liked.

STEP 4: WHISK THE GENOISE TO RIBBON STAGE

Whisk the eggs, caster sugar, salt and vanilla bean paste in a stand mixer on high for a full eight minutes, to a thick pale ribbon that holds a trail for three seconds. Genoise carries no chemical raise, so this is the only lift it gets.

STEP 5: FOLD AND BAKE THE SHEET

Sift the plain flour and cornflour together, stir through the ground sesame, and fold the dry mixture into the eggs in three additions with a large metal spoon. Fold the melted butter in last, down the side of the bowl. Spread the batter across the prepared sheet and level it to 10-11 mm deep, checking with a ruler: this is the primary structural correction, since a standard Swiss roll sheet of 6-7 mm is exactly what let the original coil collapse. Bake for 11-13 minutes, until the sponge springs back and the edges just begin to shrink from the sides.

STEP 6: ROLL THE SPONGE WARM

Turn the sponge out onto a fresh sheet of parchment dusted with caster sugar, peel off the baking parchment, and roll it loosely from the short side while still warm. Leave it rolled until completely cool. Rolling warm trains the sponge into the curve so it will not crack when you coil it for real.

STEP 7: CUT THE STRIPS AND WEIGH THE CURD

Unroll the cooled sponge, trim the edges square, and cut it lengthways into four strips of equal width, roughly 10 cm. Weigh the trimmed sponge, then beat the chilled curd smooth and weigh out half that figure - about 320 g. Weigh it rather than eyeballing it: this 1:2 filling-to-sponge ratio is the correction the judges' verdict points to. Any curd left over is excellent on toast and belongs nowhere near this cake.

STEP 8: SPREAD THIN AND BUILD THE SPIRAL

Spread the weighed curd in an even film across all four strips, about 2 mm and no more, leaving a 1 cm bare margin along one long edge of each strip - the next strip joins there and it needs to be dry to grip. Roll the first strip up tightly from one end into a firm cylinder and stand it on a board on its cut end. Wrap the second strip around the outside of the first, continuing the spiral, then join the third and fourth the same way, keeping the tension even and the top edge level.

STEP 9: CHILL IN THE COLLAR

Slide the acetate collar around the finished coil and tighten it so it just touches all round, then chill for a full hour inside the collar. This is the correction for the waistband bulge: the collar holds the girth while the curd sets hard, so the coil cannot swell outward. The original had no such support and no time to use one.

STEP 10: MAKE THE BLACK SESAME BUTTERCREAM

Whisk the egg whites and caster sugar over a pan of barely simmering water to 70C and until no grain remains between your fingers. Whip to a stiff, glossy meringue and keep going until the bowl is cool to the touch before any butter goes in. Add the unsalted butter a cube at a time, then beat in the black sesame paste and salt.

STEP 11: COAT THE CAKE

Remove the collar. Coat the cake in a thin crumb layer of buttercream, chill for twenty minutes, then apply a final smooth coat, working the palette knife vertically up the sides. A firm meringue buttercream, unlike whipped cream or a loose ganache, resists outward pressure and holds the cylinder true.

STEP 12: DECORATE AND SERVE

Press the toasted black and white sesame seeds around the base in a band, pipe a ring of buttercream rosettes around the top edge, and finish with the candied lime zest. Chill for thirty minutes, then serve at cool room temperature, cutting with a long serrated knife wiped clean between slices so the spiral reads sharply.