Preheat your oven to 350°F (175°C). In a food processor, pulse together graham crackers, light brown sugar, and melted unsalted butter until the mixture resembles moist sand. Press this mixture evenly into the bottom and up the sides of a tart pan. Bake for 10 minutes until the crust is lightly golden. Allow it to cool completely on a wire rack before filling.

In a medium saucepan, combine whole milk, granulated sugar, and vanilla over medium heat. Stir occasionally until the mixture is just simmering. In a separate bowl, whisk together egg yolks and cornstarch. Gradually add a ladle of the hot milk to the yolks while whisking continuously. Return the mixture to the saucepan, cooking over low heat for 5-7 minutes until thick and creamy.

Once the custard thickens and coats the back of a spoon, remove it from the heat. Whisk in butter for added richness. Transfer to a clean bowl and press plastic wrap directly onto its surface to prevent a skin. Refrigerate for at least 3 hours, or overnight, until completely chilled and set.

Once the custard is set and the crust is cooled, pour the silky custard into the prepared crust. Use a spatula to smooth the surface evenly. Cover with plastic wrap and return to the refrigerator until you're ready to serve.

Just before serving, pile a colorful assortment of fresh fruits atop the custard. Choose your favorites for a vibrant appeal.