In a heavy bottomed pot, brown ground beef and drain any fat. Add onion to beef and cook for a couple of minutes or until translucent {if it get too dry, add a tablespoon of oil}. Add masa harina flour to beef mixture and cook for an additional minute. You will be able to smell the corn but you don't want to over cook it. Add the beef stock and stir {the mixture will be thick}. Immediately add tomato sauce, black beans, Rotel, chili powder, cumin and salt. Stir until combined. Continue stirring occasionally until the mixture reaches a simmer. Reduce heat to medium-low and let simmer for 3 minutes, stir a couple of times so that the chili doesn't stick to the bottom of the pan. Taste, adjust seasoning as needed. Serve warm with desired toppings.