You can use leftover mashed potatoes. If you make them from scratch, use no milk or butter and reserve 3/4 cup water. Mix all ingredients except for 1 cup of the flour in the bowl of a stand mixer. Shouldn't have to tell you this but put the dry ingredients in first and mix them. Then add your liquids. Knead in the mixer for 5 minutes. Let rest. Knead again, ensuring all liquid and flour is combined. Knead until dough mass cleans sides of bowl. Rest. Remove dough mass from mixer bowl. Knead by hand a few times to get the dough malleable. Divide into two equal pieces. Using a batard (French for rolling pin) roll out the dough to slightly less than an inch thick in a rectangle with a width equal to the width of your loaf pans. The roll it lengthwise and drop it, seam-side down, into your loaf pan. (Use this trick whenever you make bread in loaves.) Repeat with the other half of the dough. Let rise, covered with a wet towel (not terry cloth, please) or oiled wax pape until dough has risen 1 inch above loaf pan. Bake at 350 for 35-40 minutes.