Bring 2 litres water to a rolling boil. Blanch the peas for 8–10 minutes or until tender. Remove the peas and refresh in cold water, drain and dry, then reserve. Do not throw away the cooking water, it provides the liquid for the soup.
In a largish casserole or saucepan (how large? Answer: large enough to accommodate the ingredients), melt the butter, add the soffritto, and sweat for 10