Saute celery, onion, and in butter for 2 minutes, transfer to a
plate and cool in the refrigerator.
2While vegetables cool, wash mushrooms and remove stems. Set caps to the
side and finely chop half of the stems. Discard the other half of the
stems or use elsewhere. Combine the sauteed vegetables, chopped mushroom
stems, and all other ingredients (except cheese slices) and mix well.
3Place mushroom caps in individual buttered casseroles or baking dishes
(about 6 caps each). Spoon 1 teaspoon of stuffing into each mushroom.
Cover with sliced cheese.
4Bake in oven for 12 to 15 minutes until cheese is lightly browned.