Heat oven to 325 F
Trim fat from steak and cut into six pieces
Season steaks with salt and pepper and place on well floured cutting board. Sprinkle more flour over the steaks and pound to tenderize. Continue to turn, flour and pound until mostly the flour is used.
Heat a large cast iron frying pan over medium heat. Add 3 TBSP vegetable oil.
When oil is hot but not smoking, add the sliced onion. Cook until onion is translucent and lightly browned. Using a slotted spoon, remove onion from the pan and set aside.
Add another TBSP of oil to the pan if needed to cover the bottom of the pan.
Place the steaks in the oil, to brown, heating in batches if necessary.
Add pan drippings (if any) to small roaster.
Add steak to roaster and cover with onions. Add the tomatoes, cover, and bake for 1½ to 2 hours or until steak is tender.
Remove, steak, tomato and onions and place on serving platter.
If sauce in roaster is too thin, place over medium heat and add the mixture of 1 TBSP flour and 1 TBSP water and cook, stirring continuously, until thickened.
Pour over steak, tomatoes and onions on platter.