Step 1

For sweet pastry, place flour on a work surface, add sugar and butter and rub in butter with your fingertips until coarse crumbs form. Add yolks, 2 tbsp iced water and a pinch of salt and lightly knead with the heel of your hand until the pastry just comes together. Flatten into a disc, wrap in plastic wrap and refrigerate to rest (2 hours). Roll out on a lightly floured surface or between 2 sheets of baking paper to a 40cm round, then trim to a neat 36cm-diameter circle. Transfer to an oven tray lined with baking paper and refrigerate until firm (1 hour).

Step 2

Combine caster sugar, lemon juice and 200ml water in a large saucepan over high heat. Add rhubarb and simmer, turning gently, until sugar is almost dissolved and rhubarb is glossy, but still firm (2-3 minutes). Refrigerate in syrup to chill (1 hour).

Step 3

Preheat oven to 190°C. For hazelnut base, pulse ingredients in a food processor until coarsely chopped. Scatter over pastry, leaving a 5cm border, then arrange drained rhubarb (reserve syrup) on top in a zig-zag pattern to form a 30cm circle surrounded by a 3cm border of pastry (trim the edge pieces to fit – the pastry will fold over the edge).

Step 4

Warm the edges of the pastry with your fingertips until pliable, then fold it over the edge of the rhubarb, pleating as you go. Brush pastry edge with beaten egg, then scatter demerara all over tart. Bake until golden and rhubarb is cooked (20-25 minutes). Serve hot with ice-cream or cream and drizzled with a little reserved rhubarb syrup.