✓ Preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper.

✓ Combine the flour, cocoa powder, and powdered sugar in a food processor. Pulse until well mixed.

✓ Add the cold, cubed butter to the dry ingredients. Process until the mixture resembles coarse crumbs.

✓ Add the egg yolk and pulse until the dough starts to come together. If necessary, add cold water gradually until the dough forms a ball.

✓ Wrap the dough in plastic wrap and refrigerate for at least 1 hour.

✓ Roll out the dough to about 1/8 inch thickness. Use a round cookie cutter or a tartlet pan to cut out circles of dough.

✓ Press the dough circles into mini tartlet pans, ensuring they are evenly coated. Prick the bottoms with a fork to prevent bubbling.

✓ Line the tartlets with parchment paper and fill with pie weights or dried beans. Bake for 12-15 minutes or until the edges are set. Remove the parchment paper and pie weights.

✓ Melt the chopped semi-sweet chocolate in a double boiler, stirring occasionally.

✓ Combine the heavy cream, granulated sugar, and unsalted butter in a saucepan. Heat over medium heat, stirring until the sugar dissolves and the mixture simmers.

✓ Remove the cream mixture from the heat and pour it over the melted chocolate. Let it sit for 2-3 minutes, then stir until smooth.

✓ Temper the eggs by gradually adding a small amount of the warm chocolate mixture, stirring constantly.

✓ Pour the tempered egg mixture into the remaining chocolate mixture, stirring until well combined. Add the vanilla extract and salt.

✓ Pour the chocolate fudge filling into the pre-baked tartlet crusts, filling them to the top.

✓ Bake the tartlets for an additional 10-12 minutes or until the edges are set and the centers are still slightly jiggly.

✓ Allow the tartlets to cool completely in the pans before transferring them to a wire rack to cool completely.