Melt the butter until bubblines, add leeks & garlic, stir and cook for 5 mins.
Add the mushrooms and continue to cook for 10 mins. stirring every few mins. Add flour & continuously stir until well mixed.
Add stock gradually, still stirring until well combined. Over high heat, bring mix to boil then reduce heat to med. low - keep cooking with the occasional stir for 10-15 mins.
Process with blender - texture depending on your taste, heat.
To serve, drizzle desired amount of cream (you won't need much, as this is quite rich) and garnish with parsley.