01 - Combine flour, powdered sugar, and salt in a bowl. Cut in cold butter with a pastry cutter or fingertips until the mixture forms coarse crumbs. Add egg yolk, mix, then slowly add cold water one tablespoon at a time until dough forms.
02 - Press dough evenly into a 9-inch tart pan with removable bottom. Prick base with a fork and refrigerate for 30 minutes.
03 - Preheat oven to 350°F. Line crust with parchment paper and fill with pie weights or dried beans. Bake 15 minutes, remove weights and paper, then bake an additional 10 minutes until golden. Let cool completely.
04 - Place chopped chocolate in a heatproof bowl. Heat cream until just simmering and pour over chocolate. Let sit 2 minutes, then whisk until smooth. Stir in butter, vanilla extract, and salt until glossy.
05 - Pour ganache into cooled crust and smooth the surface. Refrigerate at least 1 hour until set.
06 - Top with fresh berries, flaky sea salt, or whipped cream as desired before serving.