Saute the onion and celery in 1 tablespoon margarine in a saute pan until tender.
Combine the onion mixture, half-and-half, salt and pepper in a large saucepan; mix well. Heat to the boiling point, stirring occasionally.
Heat 2 tablespoons margarine in a saucepan until melted. Whisk in the flour. Cook for 3 minutes or until of roux consistency, whisking constantly. Whisk into the half-and-half mixture. Cook until thickened, stirring constantly. Add the potatoes; mix well. Cook just until the potatoes are heated through, stirring frequently.
Ladle into soup bowls. Top each serving with Cheddar cheese, bacon bits, sour cream and chives.