for this lettuce & potato soup recipe do you use raw potato or a cooked one that already soft in the centre?

INGREDIENTS 1 cup chopped onions, scallions, and/or shallots 1 garlic clove, chopped 3 tablespoons unsalted butter 3/4 teaspoon ground coriander 3/4 teaspoon salt 1/4 teaspoon black pepper 3/4 cup diced (1/3 inch) peeled potato 8 cups coarsely chopped lettuce leaves including ribs (3/4 lb) 3 cups water PREPARATION Cook onion mixture and garlic in 2 tablespoons butter in a 4- to 5-quart heavy pot over moderately low heat, stirring, until softened, 3 to 5 minutes. Add coriander, salt, and pepper and cook, stirring, 1 minute. Stir in potato, lettuce, and water and bring to a boil, then reduce heat and simmer, covered, until potato is very tender, about 10 minutes. Purée soup in batches in a blender (use caution when blending hot liquids) and transfer to a 2- to 3-quart saucepan. Bring soup to a simmer, then whisk in remaining tablespoon butter and salt and pepper to taste.

https://www.epicurious.com/recipes/food/views/lettuce-soup-231995

bon appetit