In a large bowl, stir yeast and warm water together. Let dissolve. Add the sugar, salt, softened butter and 3 cups flour. Using a stand mixer, beat until smooth. Stir remaining flour 1/2 cup at a time, until it forms a soft dough. Knead with stand mixer for about 7-9 minutes or until smooth and elastic.
Grease a large bowl. Place dough in greased bowl. Turn once to coat. Cover with plastic or a damp towel and let rise in a warm place until doubled, about 1-1/2 hours.
Press dough down. Turn out onto a lightly floured surface. Divide dough in half.
Shape each half into a loaf. Place in two greased 8 1/2 x 4 1/2 -or 9x5-in. loaf pans. Cover again and let rise until doubled, about 30-45 minutes.
Bake at 375° for 30-35 minutes or until golden brown and bread sounds hollow when tapped. Remove from pans to wire racks to cool.