Step 1: Make the Tart Dough
In a food processor, pulse together flour, powdered sugar, and salt until combined. Add the cold cubed butter and pulse 10-12 times until the mixture resembles coarse crumbs with some pea-sized butter pieces remaining. Add egg yolk and vanilla, then pulse just until the dough begins to clump together. If the dough seems too dry, add ice water 1 teaspoon at a time. Don’t overprocess—you want a crumbly mixture that holds together when pinched.

Step 2: Chill the Dough
Turn the dough out onto a piece of plastic wrap. Use the wrap to press it together into a flat disk about 1 inch thick. Wrap tightly and refrigerate for at least 1 hour or up to 2 days. This chilling time is crucial—it allows the gluten to relax and the butter to firm up for easier rolling.

Step 3: Roll and Shape the Dough
Remove dough from fridge and let sit for 5-10 minutes if very hard. On a lightly floured surface, roll the dough into an 11-12 inch circle about ⅛ inch thick. Keep lifting and rotating the dough as you roll to prevent sticking. Carefully transfer to a 9-inch tart pan with removable bottom by rolling the dough around your rolling pin, then unrolling over the pan. Gently press into the bottom and up the sides, then trim excess by rolling your pin across the top. Prick the bottom all over with a fork.

Step 4: Freeze the Shell
Place the tart shell in the freezer for 15 minutes. This prevents shrinking during baking. Meanwhile, preheat your oven to 375°F (190°C).

Step 5: Blind Bake the Shell
Line the frozen tart shell with parchment paper, making sure it comes up the sides. Fill with pie weights or dried beans, distributing them evenly. Bake for 20 minutes, then carefully remove the parchment and weights. Return to oven and bake for another 5-7 minutes until the bottom is golden brown and looks dry. If any cracks appear, don’t worry—the filling will cover them! Let cool completely on a wire rack.

Step 6: Prepare the Chocolate Ganache
Place the finely chopped chocolate in a large heatproof bowl. In a medium saucepan, heat the heavy cream over medium heat until it just begins to simmer (small bubbles around the edges—don’t let it boil!). Immediately pour the hot cream over the chocolate. Let it sit undisturbed for 2 minutes to allow the heat to melt the chocolate.

Step 7: Create Silky Ganache
After 2 minutes, whisk gently from the center outward until the mixture is completely smooth and glossy. Start slowly to create an emulsion, then whisk more vigorously. Add the butter, vanilla, and salt, whisking until fully incorporated and silky smooth. For extra-smooth ganache, strain through a fine-mesh sieve.

Step 8: Fill the Tart
Let the ganache cool for 10-15 minutes until it’s slightly thickened but still pourable (it should coat the back of a spoon). Pour the ganache into the cooled tart shell, using a spatula to spread it evenly and smooth the top. Gently tap the pan on the counter to release any air bubbles.

Step 9: Set the Tart
Let the tart cool at room temperature for about 30 minutes, then refrigerate for at least 2-3 hours until the ganache is completely set. The ganache should be firm but not hard.

Step 10: Serve and Garnish
Before serving, remove the tart from the refrigerator and let it sit at room temperature for 15-20 minutes for the best texture and flavor. Remove the outer ring of the tart pan, leaving the tart on the base for easier slicing. Dust with cocoa powder, sprinkle with sea salt flakes, or arrange fresh berries on top. Slice with a hot, dry knife (dip in hot water and wipe clean between cuts) for perfect slices.