Heirloom Tomato, Ham and Fontina Frittata

INGREDIENTS

• 12 eggs
• 1/3 cup grated Parmigiano-Reggiano cheese
• Kosher salt and freshly ground pepper, to taste
• 5 oz. Italian fontina cheese, cut into 1/2-inch cubes
• 1 Tbs. plus 1 tsp. olive oil
• 1 red onion, diced
• 5 oz. ham steak, cut into 1/2-inch cubes
• 12 oz. assorted heirloom tomatoes, cut into slices 1/2 inch thick
• 1 1/2 Tbs. thinly sliced fresh basil