Activate the yeast by combining warm water, sugar, and yeast in a large bowl. Let sit 5 to 10 minutes until foamy.
Add salt, butter, and flour one cup at a time, stirring until a shaggy dough forms.
Knead on a floured surface for 8 to 10 minutes until smooth and elastic.
Rise in an oiled bowl, covered, for 1 to 1.5 hours until doubled in size.
Shape into a log and place seam-side down in a greased 9x5 loaf pan. Cover and rise for 30 to 45 minutes.
Bake at 375°F for 25 to 30 minutes until the top is deep golden and the loaf sounds hollow when tapped.
Cool on a wire rack for at least 20 minutes before slicing.