Mix 3 ½ cups of all-purpose flour with sugar, salt, vegetable shortening and yeast in a large mixing bowl. Add very warm milk; beat for about 1 minute. Stir in enough of the remaining flour, a cup or so at a time, until dough is easy to handle.
Turn dough onto a lightly floured surface. Knead, adding more flour as necessary to keep it from sticking, until smooth and elastic, about 8 to 10 minutes. Place dough in a large buttered mixing bowl. Turn dough over so greased side is up. Cover with a clean dish towel and let rise in a warm place, out of drafts, for about 1 hour, or until doubled. When dough is touched, an indentation will remain.
Punch dough down and divide into two equal portions. Flatten each half with hands or rolling pins into a rectangle about 18x10 inches. Starting at 10-inch edge, roll dough tightly; pinch long seam together. With sides of hands, press each end of loaf; fold ends under loaf. Place loaves, seam side down, in loaf pans (approximately 9 x 5 x 3-inch). Brush each loaf lightly with butter. Cover loosely with clean dish towels and let rise until double, about 35 to 50 minutes. Preheat oven to 425°. Bake loaves on a low rack, so tops of pans are at the center of the oven. Bake for 25 to 30 minutes. Bread will sound hollow when lightly tapped.
