Heat oven to 450°F. In a large bowl, dissolve the yeast, salt, and sugar in the warm water. Gradually stir in the flour, adding only until the mixture refuses to absorb more. On a floured board, knead the dough for 3 to 4 minutes. Transfer the dough to a greased bowl and brush the top lightly with butter. Cover with a damp cloth. Set the dough aside in a warm place to rise for 1 1/2 hours, or until it is double in size. Butter a baking sheet and sprinkle it with cornmeal, shaking off the excess. Punch down the dough. Transfer the dough to a floured board and divide it into thirds. Roll each portion into a 8" x 13" rectangle. Roll each rectangle up from the long side, seal and shape ends. Place the loaves on the prepared baking sheet and with a sharp knife make several diagonal cuts across the tops. Brush lightly with melted butter. Let rise in a warm place - about 45 minutes. Place the bread on the middle rack in the oven. Place a pan of hot water on the bottom of the oven. Bake at 450°F for 5 minutes. Reduce oven temperature to 350°F and continue baking for 30 minutes. Makes 3 loaves.