Dan's Rhubarb and Custard Vertical Layer Cake

STEP 1: MAKE THE RHUBARB COMPOTE
Make this first, as it needs to cool. Combine the chopped rhubarb, granulated sugar and orange juice in a saucepan over medium heat. Cook, stirring occasionally, for 8–10 minutes until the rhubarb collapses into a soft, jammy mass. Stir in the slaked cornflour and cook for another minute or two until thick enough to hold a line when you drag a spoon through it. You want a spreadable compote, not a runny sauce — too wet and it will slump out of the spiral. Spread on a plate and chill completely.

STEP 2: MAKE THE VANILLA CUSTARD
Whisk the egg yolks, caster sugar and cornflour to a pale paste. Heat the milk with the vanilla bean paste until very hot but not boiling, then pour slowly onto the yolks, whisking constantly. Return to the pan and cook over medium heat, whisking, until very thick — about 2–3 minutes after it comes to a gentle boil. Press through a fine-mesh sieve, cover the surface directly with cling film and chill until cold.

STEP 3: BAKE THE SPONGE SHEETS
Preheat the oven to 200°C (400°F). Whisk the eggs and caster sugar to the ribbon stage — pale, tripled in volume, holding a trail for several seconds. Sift over the self-raising flour with the salt and fold gently, then fold in the melted butter and vanilla extract. Divide between two lined 33 x 23 cm (13 x 9 in) trays, spread level, and bake for 8–10 minutes until just springy. Turn each sponge out onto a sugared sheet of parchment, peel off the lining, and — while still warm and pliable — cover with a clean tea towel so they do not dry out and crack.

STEP 4: MAKE THE CUSTARD BUTTERCREAM
Beat the softened butter until pale and fluffy. Beat the cold custard until smooth, then add it to the butter a spoonful at a time, whisking until you have a silky, pipeable custard buttercream. If it looks split, keep beating — it will come together as the temperatures equalise.

STEP 5: BUILD THE VERTICAL SPIRAL
Trim each sponge to a clean rectangle and cut into long strips about 7–8 cm (3 in) wide — the width sets the height of your finished cake. Spread each strip with a thin, even layer of custard buttercream, then a thin layer of chilled rhubarb compote, leaving a small border. Roll the first strip into a tight coil standing on its end. Stand it in the centre of your serving board, then wrap the next strip around it, joining strip to strip, continuing until you have a single broad spiral disc of the desired diameter. Keep the bottom edge level as you go.

STEP 6: CHILL, THEN CRUMB-COAT
Chill the assembled spiral for 20–30 minutes to firm up — this is the single most important step for a clean finish. Make the cream cheese icing by beating the butter smooth, beating in the cream cheese just until combined (over-beating makes it loose), then the sifted icing sugar and vanilla extract. Apply a thin crumb coat over the top and sides and chill again for 15 minutes.

STEP 7: POACH THE RHUBARB RIBBONS
While the cake chills, use a mandoline or vegetable peeler to shave the slender stalks into long thin ribbons. Bring the granulated sugar, water and optional grenadine to a simmer, slip in the ribbons, and poach very gently for 1–2 minutes until just bendy but still holding their shape and colour. Lift out and lay flat on parchment to cool.

STEP 8: FINAL ICING AND DECORATION
Apply a final smooth layer of cream cheese icing over the chilled cake. Arrange the poached rhubarb ribbons vertically around the outside of the cake, letting them curl slightly at the top for movement. Chill until ready to serve, and slice with a clean, warm knife to reveal the concentric rhubarb-and-custard rings.