In a small saucepan, melt butter in milk. Let cool to warm (110 degrees) or room temperature. Into the bowl of a standing mixer with dough hook, combine milk with mashed potatoes, salt, sugar, yeast, and warm milk. Add flour and knead with dough hook (or by hand) for 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 rest about one hour or until double in size. Oil two 9 by 5 inch loaf pans. Turn dough onto a lightly floured work surface. Divide dough in half and knead 3 or 4 times. Shape into an approximately 9-inch long rectangle. Roll lengthwise into a log and place seam side down into loaf pan. Cover with plastic or a clean dry dish towel and let rise until doubled, about 1 hour. Heat oven to 375 degrees. Bake about 30 minutes, or until hollow when tapped. Turn onto wire racks and let cool completely. Serve with butter and honey.