In a small saucepan, combine the flour, salt and pepper. Gradually stir in milk until smooth. Bring to a boil over medium heat; cook and stir for 1 minute or until thickened. Reduce heat to low; keep warm and stir occasionally. , In a double boiler over simmering water, constantly whisk the egg yolk, lemon juice and water until mixture begins to thicken and coats the back of a metal spoon. Reduce heat to low. Slowly drizzle in melted butter, whisking constantly. Whisk in milk mixture. Serve immediately.