01 - In a small bowl, combine the warm milk, instant yeast, and a spoonful of sugar. Let stand for 5 minutes until the mixture becomes foamy and bubbly. In a stand mixer fitted with a dough hook, combine the all-purpose flour, remaining sugar, and salt. Add the eggs and proofed yeast mixture, then knead on medium-low speed for 5 minutes until a shaggy dough forms.
02 - Gradually add the softened butter, one tablespoon at a time, kneading continuously until each piece is fully absorbed. Continue kneading for about 10 minutes total until the dough is smooth, shiny, and elastic. Transfer to a lightly oiled bowl, cover with plastic wrap or a damp towel, and let rise in a warm spot for 1 hour or until doubled in bulk.
03 - While the dough rises, heat the milk in a medium saucepan 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 stream the hot milk into the yolk mixture while whisking constantly to temper the eggs. Return the entire mixture to the saucepan and cook over medium heat, whisking vigorously, until the custard thickens and coats the back of a spoon, about 3 to 5 minutes. Remove from heat, stir in the vanilla extract, and transfer to a bowl. Press plastic wrap directly onto the surface to prevent a skin from forming and let cool completely.
04 - Preheat the oven to 350°F. Punch down the risen dough and turn it out onto a lightly floured surface. Roll into a 12-inch round circle. Transfer to a parchment-lined baking sheet or pizza pan. Use your fingers to press a slight raised rim around the outer edge. Spread the cooled custard evenly over the dough, leaving a 1/2-inch border around the rim. Sprinkle with 2 tablespoons of granulated sugar and arrange fresh fruit over the top if desired.
05 - 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 before slicing into 8 wedges. Dust with powdered sugar just before serving.