Dissolve yeast and sugar in warm milk in a large bowl; let stand 5 minutes. Stir in butter. Lightly spoon flour into dry measuring cups; level with a knife. Add 4 1/4 cups flour and salt to yeast mixture; stir until blended. Turn dough out onto a floured surface. Knead until smooth and elastic (about 10 minutes); add enough of remaining flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in size. Punch dough down; let rest 5 minutes. Roll into a 14 x 7-inch rectangle on a floured surface. Roll up rectangle tightly, starting with a short edge, pressing firmly to eliminate air pockets; pinch seam and ends to seal. Place roll, seam side down, in a 9 x 5-inch loaf pan coated with cooking spray. Cover and let rise 1 hour or until doubled in size.
Preheat oven to 350°.
Uncover dough. Bake at 350° for 45 minutes or until loaf is browned on the bottom and sounds hollow when tapped. Remove loaf from pan, and cool on a wire rack.