In a large saucepan, heat oil over medium heat. Add leeks; cook and stir 3-5 minutes or until tender. Stir in cauliflower, thyme, garlic and Worcestershire sauce. Add broth; bring to a boil. Reduce heat; simmer, covered, 30-35 minutes or until vegetables are very tender.
Puree soup using an immersion blender. Or, cool soup slightly and puree in batches in a blender; return to pan. Add evaporated milk and cheese; cook and stir 3-5 minutes or until cheese is melted. If desired, sprinkle each serving with additional cheese and black pepper.