Snapper with breadcrumbs

1 tablespoon butter 2 lbs red snapper fillets salt white pepper 2 egg whites 2 tablespoons chopped fresh parsley Dijon mustard 1 teaspoon dried tarragon 3[...]

3/4 cup celery 1/2 onion , chopped 4 tablespoons butter , softened (or margarine) 4 cups dry breadcrumbs 1/2 cup low-fat sour cream 1/4 cup lemon , peeled and[...]