01 - In a small bowl, combine the warm milk, instant yeast, and a pinch of the measured sugar. Stir gently and let stand for 5 minutes until the mixture becomes foamy and fragrant, confirming the yeast is active.
02 - In the bowl of a stand mixer fitted with a dough hook, combine the flour, remaining sugar, and salt. Add the eggs and proofed yeast mixture. Knead on medium-low speed for 5 minutes until a shaggy dough forms. Gradually add the softened butter one tablespoon at a time, continuing to knead for 10 minutes until the dough is glossy, smooth, and elastic.
03 - Transfer the dough to a lightly oiled bowl, cover tightly with plastic wrap, and let rise in a warm, draft-free spot for 1 hour or until doubled in volume.
04 - While the dough rises, heat the milk in a medium saucepan over medium heat until steaming but not boiling. In a separate bowl, vigorously whisk the egg yolks, sugar, cornstarch, and salt until pale and thick. Slowly stream the hot milk into the yolk mixture while whisking constantly to temper. Return the combined mixture to the saucepan and cook over medium heat, whisking continuously, until thickened to a pudding-like consistency, 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.
05 - Preheat the oven to 350°F. Gently punch down the risen dough to release excess air. On a lightly floured surface, roll the dough into a 12-inch round. Transfer to a parchment-lined baking sheet or pizza pan. Using your fingertips, press and pinch a raised rim around the outer edge to form a crust border.
06 - Spread the cooled vanilla custard evenly across the dough surface, leaving a 1/2-inch border around the rim. Sprinkle 2 tablespoons of granulated sugar over the custard for caramelization. Arrange fresh berries or sliced stone fruit on top if desired.
07 - Bake on the center rack for 22 to 25 minutes until the brioche crust is deeply golden and the custard is lightly set with a gentle jiggle. Remove from the oven and allow to cool for 10 minutes on the pan.
08 - Slice into 8 wedges with a sharp knife or pizza cutter. Dust with powdered sugar just before serving. Serve slightly warm or at room temperature.