Make the Soup: In a large saucepan, melt butter over medium heat. Add garlic, celery, and onion. Cook until softened, about 5 minutes. Stir in potatoes and stock. Bring to a boil, reduce heat, and simmer until potatoes are tender, about 15 minutes.
Using an immersion blender (or transfer to a standard blender in batches), purée the soup until smooth. Stir in cream and dill. Season with salt and pepper. Keep warm on low heat.
Prep the Halibut: Season halibut with salt and pepper. Wrap each fillet with two slices of prosciutto.
Cook the Halibut: Heat olive oil in a skillet over medium-high heat. Sear halibut until golden and cooked through, about 3–4 minutes per side.
Serve: Spoon dill soup into bowls and place a halibut fillet in the center of each. Garnish with a sprig of fresh dill if desired.
🍲 Pro Tip: Serve with crusty bread or a simple green salad to round out the meal.