Sauté the onion in the butter until soft. Stir in the flour and the dry mustard. Cook for several minutes, stirring constantly. Transfer the mixture to a soup pot and stir in the broth, whisking until smooth. Add the carrots and potatoes. Simmer over medium heat for 30 minutes. Add the half-and-half. Reduce the heat to low and add the Cougar Gold cheese and stir until melted. Season with salt and pepper to taste. Sprinkle with celery leaves.
Makes 6 servings