Place a large pot over medium heat. Add butter, onion and garlic. Cook for about 2-3 minutes.
Then, add sweet potato and cook for about 1 minute.
Add water and bring to a boil.Cook until sweet potato is fork tender (about 10-15 minutes)
Add salt and pepper.
Add lettuce, stir and turn off heat.
Transfer soup to blender and blend until smooth.
Transfer soup back to pot over medium heat.Add cooking cream.Bring to a boil and then turn off heat.
Drizzle with cooking cream and sprinkle with some chili flakes.