In a double boiler, heat milk, bay leaf, and onion until hot, not boiling. Add butter and flour mixture and cook, stirring, until sauce is thickened and smooth. Remove bay leaf and onion.
For a lower fat version omit the ham and cheese from the recipe Remove the mustard to tempt fussy eaters Variations include: poaching the eggs and using the mustard as a spread on the muffins or use heated tinned tomato's and pour over the top of each muffin stack