Heat oil in 10-inch cast-iron skillet over medium heat. Add onion; cook until browned, 8 to 10 minutes, stirring often.
Stir in potatoes, salt and pepper. Add enough broth to cover potatoes. Bring to boiling. Reduce heat to medium; simmer potatoes until very tender and liquid is almost completely absorbed, 20 to 30 minutes. If potatoes become too dry, add a little more broth. If too much liquid remains, increase heat to boil away excess. Stir mixture from time to time to prevent potatoes sticking to bottom of skillet.
Heat broiler. Flatten the potatoes with back of a spatula. Sprinkle bread crumbs evenly over top. Place skillet under broiler. Broil until the potatoes are crusty and golden brown, about 2 minutes. Makes 6 servings.