Place chopped cauliflower and broccoli into the slow cooker.
Add sliced leeks and carrots.
In a medium bowl, whisk together the soup, sour cream, 1 cup cheddar cheese, mozzarella cheese, milk, and seasonings.
Pour sauce over the vegetables, and stir gently.
Place cover on slow cooker and cook on low 4-5 hours. Top with remaining cheddar cheese and allow it to melt. Serve.