Line a 10-inch (25cm) tart mold with the shortcrust pastry and prebake at 350°F (180°C) for 20 minutes.
Meanwhile, in a saucepan, bring the milk and cream to a boil.
Remove from heat, add the chocolate, and wait 2 minutes before whisking until smooth.
Without stopping whisking, add the two eggs.
Pour this mixture over the tart crust and bake at 325°F (165°C) for 15 minutes, then reduce the oven temperature to 250°F (120°C) and bake for 10 more minutes.
Cool completely and top with salted butter caramel.
Salted Butter Caramel:
In a saucepan, melt the sugar slowly to obtain caramel.
In another saucepan, heat the cream, then slowly pour it into the caramel, being careful of splatters.
Bring to a boil for two minutes to obtain a smooth mixture without lumps.
Off the heat, add the butter while constantly whisking.
Add the flaky sea salt and let cool to room temperature, whisking occasionally.