Whisk flour and sugar, then cut in butter until crumbly.
Add yolk and ice water to form dough; don’t overmix.
Wrap and chill dough 30 mins; roll out and fit into tart pan.
Line with parchment and weights; bake at 375°F for 25 minutes.
Simmer cream just until bubbling around edges.
Pour cream over chocolate; let sit 2 minutes, then stir.
Add butter, vanilla, and salt; mix until smooth and glossy.
Pour ganache into cooled crust and tap to remove air bubbles.
Refrigerate at least 2 hours or overnight until fully set.