Carefully remove the pot from the slow cooker and use a hand-held blender to blitz the soup until smooth – watch out for splashes. Stir in enough milk to reach your preferred consistency (see Tips).
Cook the bacon and remove from pan. Sauté onions and mushrooms until softened. Add the garlic and sauté a few more minutes. In the crockpot (use a liner if you can) add the mixture and remaining ...