Preheat the oven to 190°C/Fan 170°C Fan/ Gas 5.
Lightly grease your 23 x 33cm baking tin and line the base with parchment paper. Lightly flour a work surface and roll the pastry into a large rectangle, then trim it to measure 38 x 28cm. Use it to line the prepared tin, taking it up the sides. Dock the base with a fork, then refrigerate for 20 minutes, or until the pastry is firm.
Line the chilled pastry case with a crumpled piece of parchment paper that fully covers both base and sides and fill it with baking beans or rice.
Bake for about 25 minutes, then use the paper to carefully lift out the baking beans. Return the tin to the oven for 10 minutes, or until the pastry is lightly browned. Set aside while you prepare the filling.
Reduce the oven temperature to 170°C/ Fan 150°C/ Gas 3. Place the syrup, eggs, salt, lemon zest and lemon juice in a large bowl and whisk until combined. Stir in the breadcrumbs. Pour this mixture into the pastry case and bake for 20–25 minutes, or until the filling is set around the edges with just the barest of wobbles in the middle. Set aside to cool.
Once cool, use the parchment to carefully lift it from the tin and cut into slices. The tart is best served within a couple of days of baking.