Cook potatoes according to package directions.While potatoes are cooking, saute onion in a large Dutch oven.Add cooked potatoes to the onion.Add chicken stock, half-and-half, butter, and a teaspoon of salt to the pot.Bring to a simmer and cook for about 15 minutes, until butter is melted and soup thickens slightly.Stir in sour cream until completely blended into soup.Add additional salt and pepper to taste.Serve with baked potato toppings: cheese, bacon, green onions.