Preheat your oven to 350°F (175°C). In a food processor, pulse graham crackers into fine crumbs. Combine with light brown sugar, fine sea salt, and melted unsalted butter in a mixing bowl, stirring until well mixed. Press firmly into the bottom and up the sides of a tart pan. Bake for 10 minutes until lightly golden. Let the crust cool completely on a wire rack.

In a medium saucepan, heat whole milk over medium heat, adding granulated sugar, fine sea salt, and the vanilla bean or extract. Stir frequently until it simmers, then remove from heat. In a separate bowl, whisk the egg yolks and cornstarch. Gradually temper the egg mixture by slowly whisking in the hot milk to prevent curdling. Return the mixture to the saucepan and cook over low heat, stirring constantly for 5-7 minutes until thickened. Remove from heat and mix in unsalted butter, then cool completely.

Once the custard is completely cool and the crust is set, gently whip the custard until smooth. Pour it into the cooled graham cracker crust, spreading it evenly. Cover with plastic wrap, ensuring the wrap touches the surface. Chill in the refrigerator for at least 3 hours.

Just before serving, top the tart with fresh fruit. Slice into wedges and serve cold.