In the bowl of a stand mixer, combine the water, sugar, and kosher salt. Sprinkle yeast on top and allow it to rest for 15 minutes. The mixture will bubble and foam. Add flour and butter and begin to mix at low speed with the dough hook attachment. Once combined, increase speed to medium and knead for about 5 minutes. The dough should be smooth and pulling away from the sides. If it seems too wet, knead in a tbsp of flour. Remove dough to a lightly oiled bowl, cover with a lid or plastic wrap, and leave in a warm place. After 50-55 minutes, dough should be doubled in size.