Cook potato in boiling water 10 minutes or until very tender. Drain potato in a colander over a bowl, reserving 1 cup cooking liquid. Mash potato with a fork until smooth. Cool cooking liquid to 100° to 110°. Dissolve yeast and sugar in cooled cooking liquid in a large bowl; let stand 5 minutes. Lightly spoon flour into dry measuring cups; level with a knife. Add 2 1/2 cups flour, mashed potato, 3/4 cup shredded cheese, oil, salt, mustard, and pepper to yeast mixture; stir until well-blended.
Turn dough out onto a floured surface. Knead until smooth and elastic (about 10 minutes); add 1/2 cup flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover dough, and let rise in a warm place (85°), free from drafts, 45 minutes or until doubled in size. (Press two fingers into dough. If indentation remains, the dough has risen enough.) Punch dough down; sprinkle with 1/2 cup diced cheese. Knead dough until cheese is well-blended (about 5 minutes), and add enough of remaining flour, 1 tablespoon at a time, to prevent the dough from sticking to hands. Roll into a 14 x 7-inch rectangle on a lightly floured surface. Roll up the rectangle tightly, starting with a short edge, pressing firmly to eliminate air pockets, and pinch seam and ends to seal. Place roll, seam side down, in a 9 x 5-inch loaf pan coated with cooking spray. Cover and let rise 40 minutes or until doubled in size.
Preheat oven to 375°.
Uncover dough. Bake at 375° for 55 minutes or until loaf is browned on the top and sounds hollow when tapped. Remove from pan; cool on a wire rack.