Heat olive oil in large saucepan over medium heat.
Add leeks. Cook 5 minutes until softened.
Add cauliflower, garlic, thyme, Worcestershire sauce and vegetable broth. Simmer for 30 40 minutes over medium low until vegetables are very tender.
Remove from heat and either blend with an immersion blender, or in batches in a blender. If you use a blender, return the mixture to the pan and add evaporated milk and cheese. Cook over medium heat for 3 5 minutes to melt cheese.