1. Wipe the mushrooms with a damp, clean cloth and chop roughly.
2. Place into a clean bowl, cover with cling film and place into a fridge for later.
3. Peel and finely dice the shallot.
4. Keep the white sauce warm in a bain marie.
5. Weigh and measure all ingredients.
6. Place a heavy-based saucepan over a medium heat on the hob.
7. Add the butter and when melted, add the shallot and allow to sweat for a few moments.
8. Next, add the chopped mushrooms and stir-fry for about 3 minutes.
9. Carefully add the brandy.
10. Boldly ignite the pan to flambé the mushrooms. The flame will soon die away as the alcohol is quickly burnt off.
11. Stir in the mustard and white sauce and bring to a simmer.
12. Season to taste and remove from the heat.
13. Using a stick blender in your saucepan, blend the sauce until it is quite smooth and the mushrooms have broken down into the sauce.
14. Alternately, pour the liquid into a liquidizer to make a smooth sauce and return to the saucepan.
15. Return the mushroom sauce to the hob and bring back to a gentle simmer.
16. Stir in the cream, check the consistency and seasoning and serve the mushroom sauce hot.