Make the Crust: In a large bowl, whisk together the flour, powdered sugar, and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs. Gradually add the ice water, one tablespoon at a time, mixing until the dough just comes together.

Chill the Dough: Form the dough into a disc, wrap it in plastic wrap, and refrigerate for at least 30 minutes. This chilling process helps the gluten relax, resulting in a tender crust.

Roll Out the Dough: On a lightly floured surface, roll the dough into a 12-inch circle. Carefully transfer the dough to a 9-inch tart pan with a removable bottom. Press the dough into the bottom and up the sides of the pan.

Prepare for Baking: Trim any excess dough from the edges of the tart pan. Prick the bottom of the crust with a fork (this prevents it from puffing up during baking). Line the crust with parchment paper and fill with pie weights or dried beans. Blind bake in a preheated oven at 375°F (190°C) for 20 minutes.

Remove Weights and Bake Again: Remove the parchment paper and pie weights. Bake for another 10-15 minutes, or until the crust is golden brown. Let the crust cool completely before filling.

Make the Chocolate Filling: While the crust is cooling, place the chopped dark chocolate in a heatproof bowl. In a saucepan, heat the heavy cream and butter over medium heat until it just comes to a simmer. Don't let it boil!

Melt the Chocolate: Pour the hot cream mixture over the chopped chocolate and let it sit for 1 minute to soften the chocolate. Gently whisk the mixture until the chocolate is completely melted and smooth. Stir in the salt.

Pour into Crust: Pour the chocolate filling into the cooled tart crust.

Chill the Tart: Refrigerate the tart for at least 3-4 hours, or until the filling is firm. This chilling time is crucial for the truffle filling to set properly.

Serve and Enjoy!: Once chilled, remove the tart from the pan and slice. Serve chilled or at room temperature.