In a large mixing bowl, combine all-purpose flour and granulated sugar. Cut in cold, unsalted butter until the mixture resembles coarse crumbs. Add room temperature egg and knead gently until cohesive. Wrap dough in plastic wrap and refrigerate for 30 minutes.

Preheat your oven to 350°F (175°C). Roll out the chilled pâte sucrée to about ¼ inch thick, place into a tart pan, prick the base, line with parchment, and fill with pie weights. Bake for 15-20 minutes until golden brown. Cool on a wire rack.

In a medium saucepan, gently heat whole milk with seeds from vanilla beans until just simmering. Whisk together eggs and sugar until light and thick. Gradually pour warm milk into egg mixture while whisking continuously. Transfer back and cook on medium heat until thickened. Stir in unsalted butter until smooth.

Pour the pastry cream into a clean bowl and cover with plastic wrap. Allow it to cool for 30 minutes before refrigerating for at least 2 hours.

Once the tart crust is cooled and pastry cream is chilled, spread the cream evenly into the tart shell. Refrigerate for an additional 30 minutes to set the cream.

Before serving, garnish with fresh berries, almond slivers, and powdered sugar. Add mint leaves for a refreshing finish and serve immediately.