In a large saucepan or Dutch oven, melt butter over medium heat, add onions, and cook for 5 minutes, or until translucent.
Stir in the seasoning mix, cream of potato soup, half-and-half, and liquid from the clams until well-blended. Cook uncovered until heated through, but not boiling, then add the clams.
Season with pepper, to taste. Serve hot. (For a pop of color and freshness, garnish with chopped parsley.)