Whisk the eggs, cream, 1/2 teaspoon salt, and pepper in a medium bowl to blend. Set aside. Heat the oil and butter in a 9 1/2-inch-diameter nonstick ovenproof skillet over medium heat. Add the onions, peppers and sauté until crisp-tender, about 2 minutes. Raise the heat to medium-high. Add the tomato and a pinch of salt and sauté 2 minutes longer. Pour the egg mixture over the vegetable mixture and cook for a few minutes until the eggs start to set. Sprinkle with cheese. Reduce heat to medium-low and cook until the frittata is almost set but the top is still runny, about 2 minutes. Place the skillet under the broiler set to low. Broil until the top is set and golden brown on top, about 3 minutes. Let the frittata stand 2 minutes. Using a rubber spatula, loosen the frittata from skillet and slide the frittata onto a plate.