In the bowl of an electric mixer, use a spatula to mix together the milk mixture, yeast, sugar, egg, and egg yolks until well combined. Add in the salt, vanilla, and half of the flour and stir with the spatula until combined. Fit the mixer with the dough hook and gradually add the remaining flour until a dough begins to form. Only add as much flour as you need to form the dough. Knead at medium speed until the dough is smooth and doesn’t stick to the sides of the bowl, about 8 to 10 minutes. If the dough is unbearably sticky add more flour 1 tablespoon at a time.