Once the yeast has proofed, add the flour, salt, eggs, vanilla and cooled melted butter. With a stand mixer fitted with a dough hook, or by hand, knead the dough until it comes together, about 5 minutes. The dough should feel slightly sticky to the touch, but should also pull away from the bowl. If the dough is too sticky, add 1 tablespoon of flour at a time until it comes together.