Sorrel with Gravy

Pick some clean, tender sorrel leaves; wash well, changing the water. Put them into a saucepan with a little salt and water; dissolve while stirring with a spoon; throw the sorrel into a colander and when cold press it through a sieve. Put this puree with a little prepared white roux (No. 163), and cook it for a few moments while stirring; moisten with a small quantity of gravy (No. 404); reduce the puree, mixing well all the time; season and finish with a little half-glaze (No. 400).