EGG SAUCE

3/4 pint of half milk and water, 1 egg, 1 teaspoonful of cornflour, juice of 1/2 lemon, 1/2 oz. of butter, pepper and salt. Boil the milk and water, add the butter and seasoning. Thicken the sauce with the cornflour; beat the egg up with the lemon juice. Let the sauce go off the boil; add gradually and gently the egg, taking care not to curdle it. Warm up the sauce again, but do not allow it to boil.