Melt butter in a Dutch oven over medium heat; add onion, and sauté 8 minutes or until tender. Stir in cream of potato soup, milk, and pepper; bring to a boil. Add shrimp; reduce heat, and simmer, stirring often, 5 minutes or just until shrimp turn pink. Stir in cheese until melted. Garnish, if desired. Serve immediately. Serve with oyster crackers, if desired.
*1 1/2 pounds frozen shrimp, thawed; 1 1/2 pounds peeled crawfish tails; or 3 cups chopped cooked chicken may be substituted.