Melt the butter in a large saucepan over a medium heat. Cook the onions and garlic until soft but not browned, about 8-10 mins.
Add the mushrooms and cook over a high heat for another 3 mins until softened.
Stir in the gluten free flour and cook for 1-2 minutes (to enable gelatinisation).
Add the chicken stock, bring the mixture to the boil, then add the bay leaf and simmer for another 10 mins.
Remove and discard the bay leaf.
Remove the soup from the heat and blitz until smooth using a hand blender.
Reheat gently and stir through the cream.
Garnish with 1 tbsp cream, swirled, and the chopped parsley.