Beef Stew with Shiitake Mushrooms

12     new potatoes, cut into fourths (about 1.5 pounds)
1       medium onion, chopped (about 1/2 cup)                                        
1       bag (8 oz) ready-to-eat baby-cut carrots
1       package (3.4 oz) fresh shiitake mushrooms, sliced
1       can (14.5 oz) tomato sauce                                          
1       can (10 1/2 oz) condensed beef broth
1/2    cup all-purpose flour
1       tablespoon Worcestershire sauce
1       teaspoon salt
1       teaspoon sugar
1       teaspoon dried marjoram leaves
1/4    teaspoon pepper
1       lb beef stew meat, cut into 1/2-inch pieces
In 3 1/2- to 4-quart slow cooker, mix all ingredients except beef. Add beef.

Cover; cook on Low heat setting 8 to 9 hours. Stir well before serving.