A beautifully creamy soup with a subtle taste of celery. Serve with cubes of blue cheese to melt in plus crispy smoked bacon for a real Autumn or Winter treat.
Heat the oil and butter in a saucepan.
Add the prepared onions, celery stalks and garlic. Season with salt and pepper.
Cook, stirring now and then, until the vegetables are starting to soften and brown (10-15 min).
Stir in the potato and celery leaves and cook for 2-3 minutes, stirring often.
Stir in the stock and milk, put a lid on and bring to a boil. Immediately turn down the heat and simmer until the vegetables are tender (10-15 min).
Remove from the heat and, using a stick blender, liquidize until smooth.
Stir in the double cream if using and gently reheat. Taste, add more seasoning if necessary.
Divide between bowls and serve with any or all of the optional toppings.