Prep the Vegetables: Peel the sweet potatoes and cut them into 1-inch / 2. 5cm dice. Scrape and thinly slice the carrots, and slice the celery.
Simmer the Base: Place the diced sweet potatoes, sliced carrots, celery, and the bay leaf into a large pot or Dutch oven.
Pour in the water or vegetable broth.
Bring to a rolling boil over high heat, then reduce the heat to low, cover, and let it simmer gently for about 1 hour, or until the vegetables are very tender.
Blend for Smoothness: Remove the pot from the heat and discard the bay leaf. Use an immersion blender to carefully blend the soup directly in the pot until it's completely smooth and velvety. Alternatively, let the soup cool slightly and blend it in batches in a standard blender, returning it to the pot.
Finish and Serve: Stir in the salt, fresh lemon juice, paprika, butter, and heavy cream. Return the pot to low heat and gently warm through for another 5-10 minutes, being careful not to let it boil.
Taste and adjust seasoning if needed before serving hot.
Garnish with a swirl of cream, fresh chives, or toasted pumpkin seeds for added texture and visual appeal.