Measure butter into a small bowl, add hot water, salt, and sugar; stir occasionally until fat melts.
In the meantime, blend warm water with yeast in another small bowl.
Measure 4 cups of the flour into a large bowl, making a well in the center.
When water with fat is cooled to lukewarm, combine with yeast mixture and pour into flour well.
Blend ingredients thoroughly.
Measure the remaining 1 cup flour onto a board, spreading part of it into a medium-heavy layer; turn dough out onto this area.
Knead dough vigorously for 15 minutes, gradually working in a little of the flour at a time until all is absorbed by dough (if dough still feels a little sticky, add a little flour to board to prevent sticking).
At the end of 15 minutes the dough should be smooth and velvety feeling with no flour on surface.
Place dough in a deep bowl, cover, and set in warm place and let rise until doubled in size.
Knead again on a very lightly floured board to remove air.
Divide dough in 2 equal portions; shape each into a ball and flatten slightly.
To shape each loaf, roll the ball of dough out on a lightly floured board to make a circle 8 inches in diameter.
Fold circle almost in half (like a giant Parkerhouse roll); the center of the top circular edge should set back about 1 inch from the center of the bottom edge.
Make 2 slashes all the way down through folded dough (forming 3 equal sections) from the curved side; but do not slash all the way to the fold€”stop 1 1/2 inches short of it.
Set each loaf in a greased 9-inch pie pan, spreading slashes apart and letting ends of folded side extend up rim of pan.
Cover shaped loaves lightly and let rise in a warm place until about doubled in size.
Bake in a 350° oven for 1 hour or until richly browned.
Place a small pan of water in the oven with the loaves; do not put directly beneath baking bread.