Drop mushrooms (preferably sliced) into boiling water for 1-2 minutes, drain, seal in an airtight container or bag, then freeze until ready to use. Or saute in butter. Use straight from the freeze.
THE DON'T OF PREPARING MUSHROOMS:
1. Don't peel.
2. Don't soak.
3. Don't over cook.
4. Don't store in a warm place.