1. melt the butter in a heavy based saucepan, add the flour and stir in to make a roux 2. Cook this on a gentle heat for 2-3 minutes 3. Add the white wine, whisking all the time and allow to reduce 4. Ladle or spoon in your chicken stock in three parts into the pot, whisking each time so it stays smooth 5. When the stock is all incorporated, add the bay leaves, turn up the heat, continuing to stir until the sauce begins to bubble. 6. In a different bowl mix the mustard with a little of the roux to make sure you don’t get any lumps (this is called a slurry) 7. Add this back into the roux, add the cream, stir in chopped tarragon and season to taste with salt and pepper 8. Serve with chicken or a pork chop.