Heat a couple of tablespoons of water in the base of a large pan. Add the onion and potato with a pinch of salt. Sauté on a low heat with the lid on for 5 minutes.
Add the garlic and cook for another minute before pouring in the stock. Sprinkle in the chilli flakes and celery salt and stir well. Bring to the boil, then turn down the heat and simmer for 10 minutes with the lid on until the potato is soft.
Add the sweetcorn and dairy free milk. Bring back to the boil then simmer for another 5 minutes until the sweetcorn is cooked. Keep an eye on the pan though as the dairy-free milk might boil over.
Turn off the heat. Using a stick blender, whizz the soup until half is pureéd but leave a little texture. Season with salt and pepper then serve with a little extra chilli on top if you like it spicy!