Steps
1. In a food processor, pulse together flour and sugar. Add butter and pulse until mixture resembles coarse crumbs. Add egg yolk and water, pulse until dough comes together. Wrap in plastic and chill for 30 minutes.
2. Preheat oven to 375°F (190°C). Roll out dough and line a tart pan. Blind bake for 15 minutes.
3. In a saucepan, heat milk with vanilla bean and seeds. Whisk sugar, cornstarch, and egg yolks. Slowly pour hot milk into egg mixture, whisking constantly.
4. Return mixture to saucepan, cook until thickened. Strain custard and pour into baked tart shell. Bake for 20-25 minutes until set.
5. Let cool, then chill in the fridge. Serve slices dusted with powdered sugar.