Puer's Mexican Potato Soup

In a heavy dutch oven, saute onions and tomatoes in a small amount of butter. Add cubed potatoes and saute for an additional 5 minutes. Cover with water and simmer for 20-25 minutes, so that potatoes become tender. Add chilies and simmer for 10 more minutes. Then remove from heat and stir in Jack cheese so that it dissolves. Return to heat as needed to melt the cheese. If cheese becomes stringy, add a few drops of lemon juice.
I have never made this. It is a recipe my mother made when I was growing up. I added lemon juice because it works so well in my alfredo, but I haven't tested it in this soup.