4 tablespoons sugar
1/4 cup warm water (110?-115?F)
1 package dry active yeast
3 cups unbleached all-purpose flour
1 teaspoon salt
1 cup unsalted butter, cut into 1/2 inch cubes, plus 1 teaspoon soft butter for brushing top of dough
1/2 cup milk
3 large egg yolks
1 teaspoon pure vanilla extract
Rinse a small bowl in hot water to warm it. Add 1 tablespoon of the sugar and the warm water to the bowl. Sprinkle the yeast over the water. Do not stir. Cover the bowl with a saucer and let the mixture stand for 5 minutes. Stir it briefly with a fork, cover again, and let it stand for 2 to 3 minutes more, or until bubbly.
In the bowl of a stand mixer fitted with the paddle attachment, mix on low speed the 3 cups of flour, remaining 3 tablespoons of sugar, and the salt. Add the slightly firm cubed butter and continue to mix until meal-sized crumbs form, 2 to 4 minutes, depending on upon the temperature of the butter. Stop the mixer.
Using a fork, in a separate bowl, mix the milk, egg yolks, and vanilla. Add the milk mixture to the flour, along with the dissolved yeast, and mix on low speed for about 15 seconds. Stop the mixer and scrape down the side of the bowl with a rubber spatula. Mix on low speed for another 30 seconds, or until a smooth dough is formed. this is a soft dough.
Lightly butter a medium bowl for storing the dough. Empty the dough into the prepared bowl, smoothing the top with lightly floured hands. Spread a thin layer of softened butter over the top. Cover tightly with plastic wrap and refrigerate overnight.