Spray a non stick saucepan with cooking oil, add the vegetable oil and place over medium heat. Add the garlic and onion, cook until softened about 4 minutes. Add the potatoes and stock. Bring to a boil, then reduce the heat to low. Cover and simmer until the potatoes are tender, about 20 minutes. Transfer to a food processor or blender and puree, working in batches if necessary. Return the pureed soup to the saucepan. Reserve 2 tbsp of the cheese. Stir the remaining cheese, milk, mustard, salt and pepper into the soup. Simmer for 2 minutes or until the cheese melts. Garnish each bowl with parsley and a sprinkle of the reserved cheese.