Your mushroom duxelle is ready and can be used right away or kept in a sealed container in the fridge, or frozen.
Remarks
If you prefer a finer texture, chop the mushrooms very small (or mince) instead of slicing them.
This is a very old recipe, dating pack to the 17th century, invented in France by François Pierre de La Varenne, cook to the Marquis d'Uxelles, hence the name.