Put warm water in a large bowl. Sprinkle with the yeast; stir until dissolved. Add sugar and salt; stir until dissolved. Add unseasoned mashed potatoes, soft butter, eggs, and 3 1/2 cups of flour. With an electric mixer at medium speed, beat until smooth (about 2 minutes). Gradually add remaining flour; mixing with a wooden spoon or by hand, until dough is smooth and stiff enough to leave sides of bowl. Melt 1 tbsp of butter and brush over dough. Cover with double thickness of tin foil or plastic wrap. Let rise in fridge for about 2 hours or until double in bulk. Punch down dough. Refrigerate overnight. Next day turn out dough onto a lightly floured board, knead dough until smooth and elastic and blisters appear on surface (about 10 minutes). Divide dough in half and shape each half into a smooth ball about 6 inches in diameter. Place each in a 9-inch cake pan, or you can use muffin pans or square bread pans. Melt remaining 2 tbsp of butter and spread over dough. Cover with towel. Let rise in a warm place free of drafts until the dough doubles in bulk. (1 1/2 hours to 2 hours). Preheat oven to 400°F. Bake until dough sounds hollow. When bread is done, brush melted butter over cooked bread. Remove from pans.