Start by heating a little oil or butter in a large pot over medium heat. Add chopped onions and garlic, and let them cook for a few minutes until fragrant and slightly golden. Then stir in the diced carrots and celery. I like to give them about 5 minutes to soften up and build flavor.
Now it’s time to add your diced potatoes and drop in the bay leaf. Pour in the stock—vegetable or chicken, whichever you prefer. Bring everything to a boil, then reduce the heat and let it simmer gently for about 15–20 minutes. You’ll know it’s ready when the potatoes are fork-tender.
Once everything’s soft and cooked, take out the bay leaf and set aside a ladle or two of chunky vegetables if you want some texture later. Use an immersion blender to puree the soup until it’s velvety smooth. If you’re using a regular blender, let the soup cool slightly before blending in batches to stay safe.
Return the blended soup to the pot and stir in the double cream and butter. It gets creamy and luscious fast! Add a little lemon zest to brighten things up, then season to taste with salt, pepper, and any optional spices like cumin or nutmeg.
Drop the reserved veggies back into the pot and give it another few minutes on the stove. This adds a nice bit of bite to the soup. Serve it hot, garnished with chopped spring onions—or whatever toppings you like!