For 2 people, peel and boil 2 medium size potatoes. Drain the potatoes when they are done but save the liquid in which they were cooked. Mash the tubers well, add the water they were cooked in (add more liquid if necessary) and salt and pepper to taste.
Next, brown 2-2 1/2 tablespoons flour in 2 1/2 tablespoons butter, stirring constantly. Add the browned flour and butter to the potatoes and water; boil for 2 minutes while you stir.
Finally, cut a good chunk of longhorn or mild cheddar cheese into small pieces. (Fill soup bowl 1/3 full) and cover with the thick, bubbling potato-butter flour combination. Dice a quarter slice onion on top of each serving. Break out the spoons and crackers and eat it hot.