1. Prepare the Crust:

1. Preheat oven to 350°F (175°C). In a food processor, combine flour, ground hazelnuts, and sugar. Add chilled butter and pulse until mixture resembles coarse crumbs. Add egg yolk and pulse until dough comes together. Press dough into 4-inch tartlet pans and bake for 12-15 minutes until golden. Let cool.
2. In a saucepan, heat cream and milk until just simmering. In a bowl, whisk egg yolks and sugar until pale. Slowly pour hot cream mixture into yolks, whisking constantly. Stir in vanilla. Strain custard through a fine sieve.
3. Pour custard into cooled tart shells. Bake at 300°F (150°C) for 20-25 minutes until set but slightly wobbly. Chill for at least 4 hours. Before serving, sprinkle turbinado sugar evenly over each tartlet and caramelize with a kitchen torch until golden and crisp.