Lightly coat a large, nonstick pot with cooking spray, add the oil and set over medium heat. Add the onion and garlic and sauté for 5 minutes or until the onions are softened and just begin to brown.

Set aside 2 cup of the kidney beans and add the rest to the saucepan, along with the potato, stock, salt and pepper. Bring to a boil, then reduce the heat and simmer, covered, for 15 minutes.

Purée in a blender or food processor in batches. Return the soup to the saucepan and add the milk and the remaining kidney beans. Heat through.

Serve the soup in bowls, and garnish with the Parmesan and parsley.