Sopa De Feijao Preto (Black Bean Soup)

Ingredients
1 Can Black Beans
2 Quarts Beef Stock
1 Small Acorn Squash -- Diced
Salt And Pepper -- To Taste
1 Large Onion -- Thinly Sliced
1 Cup Tomato Sauce
3 Teaspoons Flour
2 Tablespoons Butter
 

Combine, beans, stock, squash, salt, pepper, onion, and tomato sauce, simmer 20 minutes. Add flour and butter, heat through, until butter is melted, stir well. remove from heat, squeeze in lemon juice and serve.