In a large pot, melt butter over medium-low heat. Stir in celery, onion, and carrot and sauté until veggies are soft, 10-15 minutes.
Sprinkle flour over vegetables and stir until well incorporated. Mix in the rest of the ingredients and cover and simmer 30-45 minutes, stirring occasionally.
Puree soup with an immersion blender or a regular blender (but be really careful! Its HOT STUFF!) until smooth. Pour blended soup back into the soup pot.
Stir in 2 cups half & half with 1/2 teaspoon curry powder. DO NOT boil once this has been added! Serve hot!
Notes
You could use whole milk, but after the 1/4 lb. of butter, why would you choose the 'lighter' option?!