Kentucky Hot Brown Soup

1/4 cup butter or margarine
1/4 cup minced onion
1/4 cup all-purpose flour
1/2 teaspoon garlic salt
1/4 teaspoon hot sauce
4 cups milk
1 cup (4 ounces) shredded sharp Cheddar cheese
1/2 cup chopped cooked ham
1/2 cup chopped cooked turkey
Toppings: crumbled bacon, chopped tomato, chopped fresh parsley

Melt butter in a Dutch oven over medium heat. Add onion; saut