Prepare the crust: In a food processor, pulse flour, sugar, and salt. Add cubed butter and pulse until mixture resembles coarse crumbs. Add egg yolk and cold water gradually until dough forms. Wrap in plastic and chill for at least 30 minutes.

1. Preheat oven to 350°F (175°C). Roll out dough and cut into circles to fit mini tartlet pans or a muffin tin. Press dough into pans, prick bottoms with a fork, and bake for 12–15 minutes or until lightly golden. Let cool completely.
2. Make the chocolate filling: Heat heavy cream until just simmering. Remove from heat and pour over chopped chocolate in a bowl. Let sit 1–2 minutes. Stir until smooth. Add butter, vanilla, and salt. Stir until glossy and fully incorporated.
3. Assemble the tartlets: Spoon or pipe the ganache into cooled tartlet shells. Chill in the refrigerator for at least 1 hour to set.
4. Garnish and serve: Top with berries, whipped cream, or other toppings before serving. Serve chilled or at room temperature.