German Goulash

Name: German Goulash
Ingredients: 1 pound stewing beef (lean, boneless cut into 3/4 inch cubes); 8 ounces button mushrooms (or cremini mushrooms, optional but recommended); 2 ounces oil (fat or 2 tablespoons cooking oil); 1 large yellow onion, finely chopped; 2 cups water (boiling water); Salt and pepper, to taste; 1/8 teaspoon paprika; 1 to 2 teaspoons cornstarch; 1 tablespoon cold water; 1 cup tomato puree (or sour cream, optional)