Plain mashed potatoes create a fantastic breakfast bread, just made for butter and jam. If you prefer your spuds enhanced with garlic, chives, blue cheese, or bacon, this recipe will give you a more flavorful bread, great for leftover turkey sandwiches.
In a small saucepan, melt butter in milk. Let cool to warm (110 degrees) or room temperature. In the bowl of a standing mixer with dough hook, combine milk mixture with mashed potatoes, salt, sugar (or honey), yeast, and warm water. Add flour and knead with dough hook (or by hand) about 5 minutes, until you have a smooth and slightly glossy dough. Place into an oiled bowl. Cover with plastic or a clean, dry dish towel, and let rise until doubled in size, about 1 hour.
Oil two 9x5-inch loaf pans. Turn dough onto a lightly floured work surface. Divide in half and knead 3 or 4 times. Shape each dough mass into a rectangle, about 9 inches long. Roll each one lengthwise into a log, and place seam side down into its own loaf pan. Cover with plastic or a clean, dry dish towel. Let rise until doubled in size, about 1 hour.
Heat oven to 375 degrees. Bake about 30 minutes, or until loaves sound hollow when tapped. Turn onto wire racks and let cool completely. Serve with butter and honey.