Melt the butter in a large saucepan over medium heat. Add the onion, celery and a pinch of salt and sauté about 2 minutes. Add the carrots, 1 teaspoon of the toasted cumin seeds (save the other ½ tsp for sprinkling over the top of the finished soup), and the pinch allspice. Bring to a boil, cover, and simmer until the carrots are very soft, about 20-25 minutes.
When the carrots are done (take one out and if they squish easily they’re done) turn the heat off under the pot. Puree the soup in a blender in batches, or with a hand blender in the pot until completely smooth and velvety. Add a teaspoon of lemon juice and salt and pepper to taste.
Serve with a dollop of sour cream or yogurt and a sprinkling of the reserved toasted cumin seeds. Calories: About 110 per cup.