For a subtle difference substitute Hubbard, acorn, or butternut squash.
Dissolve yeast in warm water. Add pumpkin, sugar, and salt. Scald milk, add butter, and stir until melted. When cool, blend with pumpkin mixture. Add flour, 1 cup at a time, to form a stiff dough. Turn out onto floured board and knead until smooth. Place in buttered bowl, turn to grease top, cover, and let rise until doubled. Punch down, knead, divide in half, and place in 2 greased 8-inch loaf pans. Cover and let rise until doubled. Bake in preheated 350 degree oven for 40 to 45 minutes.