In large bowl of an electric mixer, stir together yeast, 1 1/2 cups of the flour, sugar, and salt.
In a pan, prepare 2 servings of instant mashed potatoes according to package directions, using amounts of water, milk, butter, and salt called for on package.
Then stir in milk, melted butter, and eggs; stir until well blended.
Add potato mixture to dry ingredients and beat for 2 minutes at medium speed, scraping bowl occasionally.
Add 1 more cup of the flour and beat at medium speed for 2 minutes longer.
With a spoon, stir in 1 more cup of the flour to form a stiff dough.
Turn dough out onto a floured board; knead until smooth and satiny (5 to 20 minutes), adding flour as needed to prevent sticking.
Turn dough over in a greased bowl; cover and let rise in a warm place until doubled (1 1/2 to 2 hours).
Punch dough down, knead briefly to release air, and shape into 2 loaves.
Place each in a well-greased 9 by 5-inch loaf pan.
Cover and let rise in a warm place until almost doubled (about 45 minutes).
Bake in a 350° oven for 35 minutes or until loaves are well browned and sound hollow when tapped.
Turn out on a rack to cool.