In a large soup pot, heat the oil and sauté the garlic until softened, but not browned. Add the leeks, celery carrot, broccoli and broth. Cover and cook 10 to 15 minutes or until carrot is soft. Turn off heat and add basil, allow to wilt (keep lid on). In batches, place soup ingredients in blender and purée. Pour back in soup pot to heat slightly and add cream if desired.