1 tbsp. unsalted butter
1 medium onion (about 6 oz.), peeled and finely chopped
3 baking potatoes (about 10 oz. each), peeled and cut into 1/4-inch slices
6 c. chicken broth
1/4 tsp. celery seed
kosher salt and freshly ground black pepper to taste
buttermilk or extra chicken broth (if desired)

Melt butter in large saucepan over moderate heat. Stir in onion and cook, stirring occasionally, until onion is translucent (about 5 minutes). Add potato slices and broth; bring to boil over high heat. Reduce heat to moderate and simmer, stirring occasionally, until potatoes are almost cooked through (about 15 minutes). Add celery seed and cook 5 minutes longer, stirring frequently to break up potato slices. Gently whisk with balloon whisk until soup becomes a little smoother, but small pieces of potato should remain. Season with salt and pepper. If not serving immediately, you may want to add a little buttermilk or extra chicken broth because soup will get thicker as it stands.

Makes 6 (1-cup) servings.