01 - Combine flour, cocoa powder, powdered sugar, and salt in a mixing bowl. Add cold cubed butter and rub in with fingertips until mixture resembles coarse crumbs.
02 - Add egg yolk and ice water, mixing gently until dough comes together. Shape into a disk, wrap tightly, and refrigerate for 30 minutes.
03 - Roll out dough on a lightly floured surface to fit a 9-inch tart pan. Press dough into pan, trimming edges evenly. Prick base thoroughly with a fork.
04 - Freeze crust for 10 minutes while preheating oven to 350°F. Line with parchment paper, fill with pie weights, and bake for 15 minutes. Remove weights and bake 10 more minutes until set. Cool completely.
05 - Heat heavy cream in a saucepan until just simmering. Pour over chopped chocolate in a heatproof bowl. Let stand for 2 minutes, then stir until completely smooth. Add butter and vanilla, mixing until glossy.
06 - Pour ganache into cooled crust, smoothing the top. Refrigerate for 1 hour until fully set.
07 - Arrange fresh raspberries decoratively on top. For a glossy finish, warm raspberry jam and gently brush over berries. Dust with powdered sugar if desired.