1.Add warm milk to a large measuring cup along with 1 1/2 teaspoons of yeast and 1 tablespoon of sugar. Give it a quick mix and let it sit for about 10 minutes until it becomes frothy.
2.Into the bowl of an electric mixer with dough attachment add flour, 1/4 cup granulated sugar, salt, 3 eggs, and the yeast mixture.
3.Start off by mixing on low speed. Once the flour begins to incorporate into the dough, pick up the speed to high. You will want to continue mixing the dough on high speed until it begins to take shape, about 4-5 minutes.
4.Cut up 1/2 cup of softened unsalted butter into chunks and add them to the dough. Continue mixing the dough on high speed for 5-10 more minutes or until the dough no longer sticks to the sides of the mixer bowl. It should have a smooth elastic texture by this point.
5.Now place the dough into a lightly greased bowl sprayed with cooking spray. Cover the dough with plastic wrap and let it rise for about 1 hour or until it doubles in size.
6.Now punch down the dough and divide it into 12 equal pieces. Shape each piece of dough into round balls. Place the brioche dough balls into a 9x13 inch deep baking dish and let them proof covered for another hour.
7.Preheat oven to 350 degrees. Combine 1 egg with a teaspoon of water and brush it over each roll using a pastry brush. Sprinkle flaky salt on top of each roll.
8.Bake the rolls for about 25 minutes until golden brown.