01 - Preheat the oven to 350°F. Grease a 9-inch tart pan with a removable bottom.
02 - Whisk together flour, cocoa powder, powdered sugar, and salt. Cut in cold butter until mixture resembles coarse crumbs. Add egg yolk and ice water, mixing until dough just forms.
03 - Press dough evenly onto bottom and sides of tart pan. Prick base with a fork and freeze for 10 minutes.
04 - Bake crust for 15 minutes. Remove from oven and let cool.
05 - Heat heavy cream, milk, and butter over medium heat until just simmering. Remove from heat; add chopped chocolate and let stand 2 minutes. Stir until smooth.
06 - Whisk in sugar, vanilla, sea salt, and eggs until fully incorporated and glossy.
07 - Pour filling into cooled crust. Bake at 350°F for 15 to 18 minutes until edges are set and center is slightly wobbly.
08 - Cool tart on a 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.