In 2 quart casserole, place 1 tablespoon butter, mushrooms and green pepper.
Microwave at high (10) 4 to 5 minutes, until mushrooms are tender; stir after 2 minutes.
In 4 cup glass measure, combine remaining butter and flour.
Gradually add broth and milk, stirring constantly until smooth.
Microwave at high (10) 3 to 4 minutes, until thickened, stirring every minute.
Add mushrooms, green pepper, sherry, salt, pepper and chicken.
Microwave at high (10) 6 to 8 minutes until heated through.