Heat the butter and oil in a large skillet over medium/high heat.
Add the prepared mushrooms in an even layer to the skillet. Allow the mushrooms to cook and brown (without stirring) for 4-5 minutes. Do not add salt.
Stir the mushrooms and return them to a single layer. Cook for an additional 3-4 minutes.
Remove the mushrooms to a paper towel lined surface to cool completely.
Once fully cooled add the mushrooms to a zip top bag or a vacuum sealed bag and press them into a single layer. Seal the bag to remove the air.
Date the bag and freeze for up to 6 months.
When ready to use, thaw the mushrooms and add to your favorite cooked dish.
Notes
Can be frozen for up to 6 months.Any type of mushroom can be sautéed and frozen with this method.Do not season the mushrooms during sautéing or they will steam and not brown.