In a food processor, pulse flour, sugar, and salt. Add cold butter cubes and pulse until mixture resembles coarse meal. Add egg yolk and 2 tablespoons ice water; pulse until dough just holds together when pressed. If too dry, add more ice water 1 teaspoon at a time. Turn dough onto a floured surface, shape into a disk, wrap in plastic, and refrigerate for 30 minutes.

Preheat oven to 375°F (190°C). On a lightly floured surface, roll dough to 1/8-inch thickness. Transfer to a 9-inch tart pan with removable bottom, pressing into edges. Trim excess dough. Prick bottom with a fork. Line with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, then remove weights and parchment and bake another 5-7 minutes until golden. Cool completely on a wire rack.

Place chopped dark chocolate in a heatproof bowl. In a small saucepan, heat heavy cream over medium heat until it just begins to simmer (do not boil). Pour hot cream over chocolate, let sit 2 minutes, then stir gently until smooth. Add softened butter, vanilla, and salt; stir until glossy and fully incorporated.

Pour the warm ganache into the cooled tart crust, spreading evenly with an offset spatula. Refrigerate for at least 2 hours until ganache is set but still slightly soft.

Just before serving, arrange halved and whole strawberries on top of the set ganache in a decorative pattern. Dust with powdered sugar and garnish with mint leaves if desired.