In a food processor, combine flour, cocoa powder, sugar, and salt. Add cubed butter, pulsing until the mixture resembles coarse crumbs. Gradually pour in the milk and blend until a dough forms. Chill for at least 3 hours.

Roll out the dough on a floured surface to about 3mm thickness. Transfer to a tart pan, press into edges, dock with a fork, then blind bake at 180°C for 25-30 minutes. Cool for 15 minutes before removing from pan.

Melt granular sugar in a saucepan over medium heat until deep amber. Add butter and cream, whisking until smooth. Stir in vanilla and sea salt, then let cool slightly before pouring into the cooled crust. Refrigerate for 1-2 hours.

Heat double cream until bubbling, pour over chopped chocolate in a bowl, then whisk until smooth. Once the caramel sets, pour the ganache over it. Chill until ganache firms up, about 1 hour.

Slice with a sharp knife and serve with whipped cream or vanilla ice cream.