Melt the butter in a heavy based saucepan, add the flour and stir in to make a roux

Cook this on a gentle heat for 2-3 minutes

Add the white wine, whisking all the time and allow to reduce

Ladle or spoon in your chicken stock in three parts into the pot, whisking each time so it stays smooth

When the stock is all incorporated, add the bay leaves, turn up the heat, continuing to stir until the sauce begins to bubble

In a different bowl mix the mustard with a little of the sauce to make sure you don't get any lumps (this is called a slurry)

Turn down the heat and cook for another 10 to 15 minutes

Add this back into the sauce, add the cream, stir in chopped tarragon and season to taste with salt and pepper

Serve with chicken or a pork chop