Portobello Steak and Scallion Potato Tower

Name: Portobello Steak and Scallion Potato Tower
Ingredients: 8 to 9 small to medium size portobello mushrooms, stems removed; Olive oil for grilling; Salt and pepper; 1/2 cup balsamic vinegar; 4 to 6 medium- sized yukon gold potatoes; 3 to 4 tablespoons butter; 1 cup heavy cream; 1 bunch scallions sliced thin, approximately 1/2 cup; 1 teaspoon chopped garlic; 2 1/2 cups balsamic vinegar; 2 ears of corn; 2 cups mesclun greens for garnish; 1 small red onion sliced very thin; 1 small bunch chives, cut into 2-inch sticks