1 ½ lbs. portabella mushrooms
1 ½ lbs. cremini mushrooms
3 large shallots
½ cup unsalted butter
4 scallions (green part only)
½ cup balsamic vinegar
5 T. soy sauce
¼ cup sugar
Halve portabellas and cut into ¼ inch thick slices. Cut cremini into ¼ inch slices. Chop shallots.
In a 12-inch heavy skillet cook half the shallots in half the butter over moderate heat, stirring 1 minute. Add portabellas and salt and pepper to taste. Cook stirring occasionally, until liquid mushrooms give off is evaporated, about 15 minutes. Transfer portabellas to a bowl and keep warm, covered.
Cook remaining butter and shallots, stirring for one minute. Add cremini mushrooms and cook stirring occasionally until liquid evaporates, about 10 minutes. Add portabellas to cremini and keep warm, covered. Mushrooms may be prepared up to this point 1 day ahead, covered and chilled.
Diagonally cut scallions into thin slices. In a bowl, whisk together vinegar, soy sauce, sugar. Heat mushrooms over medium-high heat until hot and add vinegar mixture. Boil for 3 minutes or until liquid is reduced slightly and stir in scallions.