2 tbsp. butter
1/2 lb. mushrooms, sliced
1/2 tsp. pepper
4 bakery croissants
4 tsp. mustard
1/2 lb. thinly sliced roast beef
1 lg. tomato, thinly sliced
1/2 lb. Swiss cheese

Saute mushrooms with pepper in hot butter until tender and lightly browned, about 5 minutes. Preheat oven to 375 degrees. Slice croissants in half, lengthwise. Spread bottom half with 1 teaspoon mustard; top with roast beef, mushrooms, tomato and cheese slices. Replace tops of croissants. Place on cookie sheet; cover loosely with foil. Bake for 15 minutes or until cheese is just melted and sandwich is heated through.