Sweet peas pair here with fresh mint in a silken green soup that's as elegant as it is tasty. The shells of the peas are used to boost the flavor of the soup, and the fresh mint adds a subtle under-note. If you enjoy the bold taste of mint, by all means add more! Alternately, you could substitute a few sprigs of fresh dill for the mint. The soup is versatile and tastes wonderful served either hot or cold.
Shell the peas and set aside. Reserve about 3 cups of the freshest, cleanest pods for the stock.
Wash the pods thoroughly and then slice them into 1-inch pieces. Place the stock and the pods in a large pot and bring to a boil over high heat. Reduce the heat to medium and simmer, covered, for 10 minutes. Strain and discard the pods.
Melt the butter in a large pot and sauté the leeks over medium-high heat until they soften, about 5 minutes. Add the pea stock, then increase the heat to high and bring to a boil. Add the peas and the mint; when the soup returns to a boil, reduce the heat to medium. Simmer for 8 to 10 minutes or until the peas are tender enough to purée (fork mashable).
Purée the soup in small batches in a blender until very smooth. Transfer the soup to a fine sieve set over a bowl and discard any puree that's too coarse to pass through the sieve.
Add the sugar and taste to see if the soup needs salt. Reheat if you're serving the soup hot; otherwise, refrigerate until it's thoroughly chilled.
Serve with a sprinkling of fresh mint leaves, if you like.