01 - Preheat oven to 350°F. Grease a 9-inch tart pan with removable bottom.
02 - Combine flour, cocoa powder, powdered sugar, and salt in a bowl. Cut in cold butter until mixture resembles coarse crumbs. Add egg yolk and ice water; mix until dough forms.
03 - Press dough evenly into tart pan bottom and sides. Prick base with fork. Freeze for 10 minutes.
04 - Bake crust for 15 minutes at 350°F. Remove from oven and cool.
05 - Warm heavy cream, milk, and butter in saucepan over medium heat until simmering. Remove from heat, add chopped chocolate, and let stand for 2 minutes. Stir until smooth.
06 - Whisk in sugar, vanilla, salt, and eggs into chocolate mixture until glossy and combined.
07 - Pour filling into cooled crust. Bake at 350°F for 15 to 18 minutes until edges set but center remains slightly wobbly.
08 - Cool tart on wire rack, then refrigerate for at least 1 hour until firm.
09 - Top with fresh raspberries and dust with powdered sugar if desired before serving.