"A curd, cake and crumble all in one," says Stone. "Lemon
curd forms on the bottom with a thin, spongy layer of cake on top.
A sprinkling of citrusy crumble over the cake provides a little
90 gmbutter, melted and cooled, plus extra, softened, for brushing330 gm (11/2 cups) caster sugar, plus extra for dusting3 tsp finely grated Meyer lemon rind (see note) 4eggs, at room temperature, separated 70 gm plain flour 1 tsp baking powder 300 ml milk 120 ml Meyer lemon juice (see note)Thick cream or vanilla ice-cream, to serveLemon crumble 110 gm (¾ cup) plain flour 55 gm (¼ cup) caster sugar 50 gm unsalted butter, diced and frozen 2 tsp finely grated Meyer lemon rind (see note) ¾ tsp baking powder
Preheat oven to 180C and line a baking tray with baking paper. For lemon crumble, combine flour, sugar, butter, lemon rind, baking powder, ¼ tsp sea salt and 1 tsp cold water in a bowl, then rub with fingertips until small and medium-sized clumps form. Spread on baking tray and freeze until firm (10 minutes), then bake until golden brown (12-15 minutes). Set aside.
Brush a 25cm cast-iron frying pan or ovenproof dish with softened butter and dust with sugar. Whisk rind and 220gm sugar in a bowl with an electric whisk until sugar is wet and fragrant, then add yolks and whisk until creamy (1-2 minutes). Whisk in melted butter, then sieve in flour and baking powder and whisk until smooth. Whisk in milk and lemon juice and set aside.
Whisk eggwhites and a pinch of salt in an electric mixer until foamy, then gradually add remaining sugar and whisk until soft peaks form (3-4 minutes). Fold half into lemon batter with a whisk, then fold in remaining eggwhite. Pour into prepared pan or dish and place in a roasting pan. Place in oven, then pour in enough boiling water to come halfway up the sides of pan and bake until the top just sets (20 minutes). Scatter crumble on top and bake until golden brown and just set (15-20 minutes). Remove pan from water, stand for 5 minutes and serve warm with cream or ice-cream.