Take a scant 1/2 cup good butter. Beat the butter to a cream and add the yolks of 3 eggs, beating them into the butter with the juice of 1/2 lemon. Add 1 sliced onion, 6 peppercorns and 1 bay leaf. Set the bowl containing the sauce in a basin of boiling water and stir it continually for a few moments. Then add a little boiling stock with a little grated nutmeg and 1 teaspoonful of salt. Con tinue stirring it for about 5 minutes longer, when it should be of the consistency of a custard and perfectly smooth. Strain it through a sieve, add 1 teaspoonful butter and serve.