Pour the warmed milk into a large glass or metal bowl and stir in the instant yeast and 1 tablespoon of the granulated sugar; let sit about 3 minutes until bubbly and foamy.
Stir in the softened butter, kosher salt, the remaining sugar, and 4 cups of the all-purpose flour until the dough starts to pull away from the sides of the bowl.
If the dough is still sticky, add additional flour 1/4 cup at a time (up to the 4 3/4 cups total) until it is manageable and slightly tacky.
Turn the dough onto a lightly greased counter and knead by hand about 8–12 minutes, until smooth and elastic.
Place the dough in a lightly greased bowl, cover with plastic wrap, and set in a warm, draft-free spot to double in bulk, about 1½–2 hours.
After the first rise, turn the dough onto the counter and shape into one loaf to fit a 13-inch loaf pan (or two loaves for two pans).
Lightly grease the loaf pan(s), place the shaped dough inside, cover loosely with plastic wrap, and let rise until the dough is within about 1 inch of the pan lip, about 15–20 minutes; preheat the oven to 350°F while the dough rises.
Remove the plastic wrap and bake until an instant-read thermometer inserted into the center registers 190°F, about 40–45 minutes.
Turn the baked loaf onto a cooling rack and cool completely before slicing.