In a skillet melt the butter and then add cauliflower and leeks and cook for 5 min over medium heat.Stir in mushroom and cook for 2-3 minutes.Stir in flour and cook for 1 minute.Slowly whisk in 1 cup of chicken broth, scraping up any brown bits from skillet, then transfer to slow cooker.Stir in remaining broth.Cover and cook until cauliflower is tender (4-6 hours on low or 3-4 hours on high)Stir in cheddar cheese gradually until meltedStir in cream and let sit until heated (5 minutes)Season soup with salt and pepper to taste and serve topped with cheese, bacon and green onions