For the beef, recipe states Cube Steak, which means it has been tenderized either by pounding or mechanically. Cube steak is normally made from the Round or Top Round cut. The larger Tesco stores in the larger cities more than likely carry Round cuts of beef. The Tesco website (Bangkok) shows Beef Round cut for 135 Baht/220 gram piece. I would start with 2 pieces of that and pound it yourself with a meat tenderizer.
You will want to get everything prepped and ready first before you begin cooking. Start by cutting the tenderized round cut into large pieces, maybe 3 pieces per 220 gram cut, set aside. Next cut the onion into slices and separate into rings, set aside.
In a large cast iron pan, or large non-stick skillet, add your cooking oil, between 1/4 to 1/2 inch deep, turn on heat to medium low and let it get hot but not smoking.
While the oil is heating, mix the flour on a plate along with salt and pepper to your liking. Flour the beef pieces and set aside. Add more flour to the pan as needed. Do not discard the flour.
Fry the beef pieces until brown on each side, do not over crowd the pan, so may 3 pieces at a time. Watch them closely so they do not stick to the bottom of the pan. Remove the first batch from the pan and set aside on a plate. While frying the last pan of steak throw in the onions and let them cook with the steak. Remove the onions along with the steak to the plate after frying.
Once all the pieces are fried and removed, pour out oil leaving about 1/8" inch the pan, enough to cover the bottom. Then add three heaping tablespoons of the flour mixture left over from the meat into the hot oil. Stir constantly until the flour & oil turn a deep brown color. Then add 2 cups of cold water all at once. Continue to stir as mixture thickens then reduce heat to low. Add back in the meat & onions and let it all cook on very low heat for about 30 minutes. If the gravy starts to get too thick add a little water to it. Last add salt and pepper liberally. Serve with mashed potatoes and the gravy spooned over the beef and potatoes. Our Fried Corn recipe would be a perfect side for this dish.