1. In a food processor, combine flour and powdered sugar. Add cold butter and pulse until mixture resembles coarse crumbs.

2. Add egg yolk and 1 tablespoon cold water; pulse until dough begins to come together. Add extra water if needed.

3. Form dough into a disk, wrap in plastic, and chill in the fridge for at least 30 minutes.

4. Preheat oven to 350°F (175°C). Roll out chilled dough on a floured surface to about 1/8-inch thickness.

5. Cut dough into rounds to fit mini tart pans or a muffin tin. Press dough into the pans evenly.

6. Prick the bottom of each crust with a fork to prevent puffing. Bake for 12-15 minutes or until golden. Let cool completely.

7. Heat heavy cream in a saucepan until just simmering. Remove from heat and pour over chopped chocolate in a heatproof bowl.

8. Let sit for 2 minutes, then stir until smooth and glossy. Stir in butter, vanilla, and salt until fully incorporated.

9. Pour ganache into cooled tart shells. Chill in the fridge for at least 2 hours or until set.

10. Serve chilled, optionally garnished with fresh berries or a sprinkle of sea salt.