Peel the cucumbers and steam until tender (about 20 min.). Drain well and cut into 1-in. slices. Melt the butter in a saucepan, put in the shallot and cook it without browning. Add the sliced cucumber, toss over heat for a few minutes, then stir in the white sauce. Just before boiling-point is reached, add the well-beaten egg and parsley, s