In the base of a stand mixer, whisk together the yeast, water, and 1 teaspoon of sugar. Let it rest for 5 to 7 minutes. Add the flour, milk, remaining sugar, salt, eggs, and vanilla. Knead the dough for 4 to 5 minutes until well combined. Cover with a kitchen towel and let rest for 10 minutes. Make a hole in the middle of the dough and add the room temperature butter in the middle. Knead the dough for 10 minutes. Cover with a kitchen towel and let rest for 5 to 6 minutes. Continue to knead until the dough should look smooth and no longer stick to the bowl. If it is not ready, continue to knead and rest periodically until it is ready.