Cook potatoes in 1/2 cup water until soft. Strain cooking liquid into bowl and save. Mash potatoes and set aside.
In a small bowl, combine the 3/4 cup warm water, sugar and yeast. Gently stir to combine and set aside for 5-6 minutes to "bloom".
Meanwhile, in a very large bowl, combine the flour, sugar and salt. Add the water, potatoes, butter and yeast mixture. Mix well with a wooden spoon. (At this point, if the mixture seems dry add a little more water. If the mixture is too wet, add a little more flour.)
Mix with hands and knead for about 2-3 minutes to incorporate all of the ingredients. Mixture will be slightly sticky but should not stick too much to side of bowl.
Cover and let rise in a warm draft-free place for 1 hour or until doubled in size.
Punch down dough and knead for 2-3 minutes using additional flour as needed to prevent sticking. Dough should feel smooth and elastic. Place in a greased bowl and turn dough to coat. Cover and let rise for 1 hour or until doubled in size.
Punch down dough and knead for 2-3 minutes using additional flour as needed to prevent sticking.
Divide dough in half and form each half into a round loaf. Place each loaf on a parchment-lined baking sheet that has been sprinkled with cornmeal.
Cover and let rise 1 hour. Heat oven to 350 degrees F.
When ready to bake, cut an "X" on top of each loaf. Bake for 35-45 minutes or until golden brown and sounds hollow when tapped with fingertip.
Brush each loaf with melted butter and cool on wire rack.
To store, wrap in waxed paper and then place in a plastic bag.
****Note**** 1 2-ounce cake of yeast is equivalent to 1 strip (3 1/4-ounce packets) of active dry yeast.