Make the pastry. Sift the flour and icing sugar into a bowl. Rub in the cold butter with your fingertips until the mixture resembles coarse breadcrumbs. Beat the egg and add to the mixture, working it together gently until a ball of dough forms — don't overwork it or the pastry will be tough. Pat into a thick flat disc, wrap in clingfilm and refrigerate for 30 minutes.

Preheat your oven to 180°C. On a lightly floured surface, roll the pastry out to about 4mm thick and use it to line a 25cm loose-bottomed tart tin, pressing into the sides and leaving a slight overhang. Line with baking paper, fill with baking beans or uncooked rice, and blind bake for 15 minutes. Remove the paper and beans and bake for a further 5 minutes until the base is lightly golden.

Make the filling. Warm the 600g golden syrup in a medium saucepan over medium-low heat until it starts to bubble. Add the cornflakes, scrunching some and leaving some whole, along with the breadcrumbs. Mix well. Remove from the heat and allow to cool slightly.

Beat the egg and stir it through the cooled syrup mixture.

Spread the raspberry jam evenly across the blind-baked pastry case. Spoon the syrup and cornflake mixture over the jam, spreading evenly to the edges. Bake for 20–25 minutes until the top is golden and just set.

Make the custard. Whisk the custard powder and sugar together in a small bowl with a splash of the cold milk until smooth. Heat the remaining milk in a saucepan until just simmering. Pour the custard paste into the hot milk, whisking constantly until thickened. Stir in the rum.

Drizzle the reserved tablespoon of golden syrup over the warm tart. Slice and serve with the rum custard, and a pinch of cinnamon if you like.