French Carrot Soup

"I love this soup, which is pure and full flavored. I make it often." -- From "French Farmhouse Cookbook" by Susan Hermann Loomis.

1 pound carrots, peeled, trimmed, and cut into 1/2-inch rounds (you can just throw in a bag of baby carrots)
1 medium potato, starchy such as russet, or all-purpose such as Yukon Gold, peeled and cut into quarters
5 cups water
Sea salt
1 tablespoon unsalted butter
Freshly ground black pepper

1. Place the carrots, potato, water, and salt to taste in a large saucepan and bring to a boil over medium-high heat, covered. Reduce the heat to medium and cook until the carrots are tender, 25 to 30 minutes.
2. Transfer the vegetables and 1 cup of the cooking liquid to a food processor and purée. Return the purée to the pan and add the butter, stirring until it has melted. Season to taste with salt and pepper, and serve immediately. 4 servings.