**Make the Pastry:** In a mixing bowl, combine the flour and sugar. Rub in the butter with your fingertips until the mixture resembles breadcrumbs. Add cold water, one tablespoon at a time, and mix until a dough forms. Wrap the dough in plastic wrap and chill for 30 minutes.

**Blind Bake the Pastry:** Preheat your oven to 375°F (190°C). Roll out the pastry on a lightly floured surface and line a 9-inch tart tin. Trim the edges and prick the base with a fork. Line with parchment paper and fill with baking beans or pie weights. Bake for 15 minutes, remove the weights, and bake for another 10 minutes until golden. Let cool.

**Make the Butterscotch Filling:** In a saucepan, melt the butter over medium heat. Stir in the brown sugar and cook for 2–3 minutes until smooth and bubbling. Whisk in the flour and cook for 1 minute. Gradually add the milk, whisking constantly to avoid lumps. Cook until the mixture thickens, about 5 minutes. Remove from heat and stir in the heavy cream and vanilla extract.

**Assemble the Tart:** Pour the butterscotch filling into the cooled tart shell and smooth the top with a spatula. Allow the tart to set at room temperature for 1–2 hours or refrigerate for 30 minutes.

**Serve:** Slice and serve as is or with a dollop of whipped cream for extra indulgence.