01 - Combine flour, salt, and sugar in a large bowl. Incorporate chilled butter using a pastry blender until mixture resembles coarse crumbs. Add egg yolk and gradually mix in cold water until dough forms. Flatten into a disk, wrap in plastic, and refrigerate for 30 minutes.
02 - Roll chilled dough to 1/8-inch thickness. Cut into circles fitting 3-inch tartlet pans. Press into pans, trim edges, and prick bases with a fork. Refrigerate for 10 minutes before lining with parchment and adding pie weights. Bake at 375°F for 15 minutes, remove weights, and bake an additional 10 minutes until golden. Cool shells completely.
03 - In a saucepan over medium heat, warm heavy cream until just simmering. Remove from heat and pour over chopped chocolate and butter in a bowl. Let sit for 2 minutes; whisk until smooth and glossy.
04 - Divide ganache evenly among pastry shells. Refrigerate 20 minutes to set slightly.
05 - Arrange fresh raspberries on each tartlet, pressing gently into ganache. Dust with powdered sugar.