For this dish it is absolutely essential that the peas should be very young, fresh and tender. However long old peas are cooked in this manner they never seem to get tender.
Put the peas in a thick saucepan or in an earthenware casserole with a close-fitting lid. Add the lettuce, the onions, carefully peeled, the sugar, butter and water, salt and pepper. Cover, bring to the boil and simmer, but not too gently, for 35 minutes till the peas are quite tender and till the liquid is greatly reduced. Put the peas on a hot dish, divide the lettuce and put it on the peas. Garnish with the little onions.