01 - In a small bowl, combine the warm milk, instant yeast, and a spoonful of sugar. Let the mixture rest for 5 minutes until it becomes frothy and activated.
02 - Using a stand mixer fitted with a dough hook, combine the flour, remaining sugar, salt, eggs, and proofed yeast mixture. Knead on medium speed for 5 minutes until a shaggy dough forms. Gradually add the softened butter in small pieces, continuing to knead until the dough becomes shiny, smooth, and elastic, approximately 10 minutes. Cover the bowl and allow the dough to rise for 1 hour or until doubled in volume.
03 - In a saucepan, heat the milk over medium heat until steaming but not boiling. In a separate bowl, whisk together the egg yolks, sugar, cornstarch, and salt until the mixture turns pale and smooth. Slowly pour the hot milk into the yolk mixture in a thin stream, whisking constantly to temper the eggs. Return the mixture to the saucepan and cook over medium heat, whisking continuously, until thickened to a pudding-like consistency, about 3 to 5 minutes. Remove from heat, stir in the vanilla extract, and press plastic wrap directly onto the surface to prevent a skin from forming. Let cool completely.
04 - Preheat the oven to 350°F. Punch down the risen dough to release air bubbles. On a lightly floured surface, roll the dough into a 12-inch round circle. Transfer to a parchment-lined baking sheet or pizza pan. Using your fingertips, press and pinch a slight raised rim around the outer edge to hold the custard filling.
05 - Spread the cooled custard evenly over the dough surface, leaving a 1/2-inch border around the rim. Sprinkle the top with 2 tablespoons of granulated sugar for caramelization. Arrange fresh berries or sliced stone fruit over the custard if desired. Bake for 22 to 25 minutes, or until the edges are deep golden brown and the custard is lightly set. Allow to cool slightly before slicing into 8 wedges. Dust with powdered sugar just before serving.