Preheat a pot of vegetable oil to 375° F.
For traditional chile rellenos, begin with four poblano chiles that have their stems intact.
Roast the peppers over a gas flame on the stove, on a grill, or under a broiler until charred all around. Or drop them in a deep fryer until the skins are blistered.
When cool enough to touch remove the skin. Do not remove the stems.
Make a small slit in the side of each chile and scrape out the seeds. Fill each chile with about ⅓ cups of the picadillo.
Poke the optional cheese in, if using. Do not overfill the pepper. Leave enough room that you can close the slit and make a small flap. Thread the slit in each pepper with toothpicks to close it.*
Dredge each stuffed Chile lightly in flour.
Holding the stem, dip each Chile into the batter, let some of the excess drain back into the bowl, and then carefully place in the hot oil.
Fry until they are a deep golden color, turning them once, for about four minutes.
Serve with the chile-tomato sauce.