Turn resulting dough onto lightly floured surface and knead, incorporating rest of flour. Cover with towel and let rise 1 hour. Punch down, and knead 10 times. Split tops with sharp knife and insert butter and Jack cheese. Place loaves in cold oven.
Bread is done if it sounds hollow when tapped with a knuckle.
Scrub potatoes, slice and boil in water to cover until soft. Stir in brown sugar and cool to lukewarm. Sprinkle yeast over, stir to dissolve and let rest at room temperature 45 minutes. Let rest at room temperature 45 minutes. Mound remaining flour on board, turn dough out and, using a steel baker's scraper, knead in the flour until dough is stiff enough to knead by hand.