Prepare the Pastry Crust:

In a bowl, mix flour and sugar. Add the chilled butter and rub it in with your fingers until the mixture resembles breadcrumbs.

Gradually add cold water, one tablespoon at a time, mixing until the dough comes together.

Wrap the dough in plastic wrap and refrigerate for 30 minutes.

Preheat the oven to 350°F (180°C). Roll out the dough on a floured surface and line a 9-inch tart tin. Prick the base with a fork.

Line the pastry with parchment paper and fill with baking beans or rice. Bake for 15 minutes, then remove the paper and beans and bake for another 10 minutes until golden. Let cool.

Make the Butterscotch Filling:

In a saucepan over medium heat, melt the butter, brown sugar, and golden syrup, stirring until combined.

Stir in the flour and cook for 1-2 minutes until the mixture thickens slightly.

Gradually whisk in the milk, ensuring no lumps form. Cook, stirring constantly, until the mixture thickens to a custard-like consistency.

Assemble the Tart:

Pour the butterscotch filling into the cooled pastry shell and smooth the top.

Refrigerate for at least 2 hours, or until set.