Make the pastry. In a bowl, whisk the flour, sugar, and salt.Rub in the cold butter with your fingertips until it looks like coarse breadcrumbs with a few pea-sized bits. Sprinkle in ice water, 1 tablespoon at a time, mixing just until the dough clumps together.

Chill and roll. Press the dough into a disc, wrap, and chill for 30 minutes. On a lightly floured surface, roll it into a circle about 1/8 inch thick.Line a 9-inch tart tin with the pastry, pressing into the edges. Trim the excess and chill for 15 minutes.

Blind bake the shell. Heat the oven to 375°F (190°C). Prick the base with a fork, line with parchment, and fill with baking beans.Bake for 12 minutes. Remove beans and parchment, then bake for another 5 minutes until the base looks dry. Set aside to cool slightly. Lower the oven to 350°F (180°C).

Prepare the breadcrumbs. Tear fresh white bread into pieces and pulse in a food processor until fine, fluffy crumbs form. Avoid using stale or toasted bread here; you want soft crumbs that absorb well.

Warm the syrup. In a small saucepan, gently warm the golden syrup until pourable (don’t boil). Stir in lemon juice, lemon zest, vanilla (if using), and a pinch of salt.

Mix the filling. In a bowl, whisk the egg and cream.Pour in the warm syrup mixture and whisk to combine. Stir in the breadcrumbs until evenly coated. The mixture should be thick but spoonable.

Fill the tart. Spoon the filling into the warm pastry shell and smooth the top.It will level out as it bakes.

Bake. Bake at 350°F (180°C) for 25–30 minutes until the edges are set and the center has a slight wobble. The top should be golden with a gentle sheen.

Cool and serve. Let the tart rest for at least 20 minutes before slicing. Serve warm or at room temperature with cream, custard, or ice cream.