makes 15 squares
175g plain flour, plus extra
100g caster sugar
50g ground walnuts
¼ tsp ground cinnamon
175g unsalted butter, at room temperature, chopped
2 egg yolks, lightly beaten Finely grated zest of 1 lemon
¼ tsp lemon juice
375g plum jam
Preheat the oven to 180°C/gas 4. Grease a 26x18cm shallow rectangular tin. Combine the flour, sugar, walnuts, cinnamon and butter. Add the yolks, lemon zest and juice, mixing together.
Lightly knead to form a smooth dough. Cut off a quarter of the dough (approximately 140g) to use for the lattice top, wrap tightly and refrigerate for 15 minutes. With lightly floured hands, break off and press pieces of the remaining dough into the prepared tin until the base is evenly covered. Spread the jam evenly on top, from edge to edge.
Remove the lattice dough from the fridge. Roll out on a f loured board into a long rectangle of pastry about 3mm thick. Place the board and pastry in the fridge for another 15 minutes. Cut the pastry into equal-width strips, between 5 and 10mm wide, and arrange these in a lattice pattern on top of the jam. Bake for 40 minutes or until golden brown. Allow to cool before removing from the tin. Cut into squares to serve.