2Wipe the mushrooms with a damp paper towel, remove the stems, and chop finely. Place the mushrooms, cup side up, on a baking sheet.
3In a bowl, combine the stems, cheese, tomatoes, basil, salt and pepper, and egg yolks. With an electric mixer, beat the egg whites until stiff peaks form. Fold into the cheese mixture, then spoon onto the mushrooms.
4Bake for 20 to 25 minutes, until the cheese is browned.
5Serves 8 as a first course,
Serves 4 as a side dish.