Preparation

• Prepare a medium-high (400°F to 475°F) charcoal or gas grill fire. Rub each onion slice with a little olive oil, and grill, turning occasionally, until tender with some grill marks, about 8 minutes. Remove from the grill and coarsely chop.
• In a 12-inch skillet, heat 1 Tbs. of the butter and the olive oil over medium heat. Add the shiitake, and season well with salt. Cook, stirring occasionally, until lightly browned and almost tender, 3 to 4 minutes. Add the corn, onion, and the remaining 1 Tbs. butter, and cook, tossing occasionally, until the corn is tender, 2 to 3 minutes. Stir in the balsamic vinegar, season to taste with salt, pepper, and more vinegar, and serve.