Preheat oven to broil.
In an ovenproof 10-inch skillet, over medium heat, allow oil and butter to melt and come to a medium high heat. Add onion, pepper and garlic and cook until vegetables are transparent, not browned. Stir in cooked sausage.
In a bowl combine eggs and whisk until light a fluffy. Add salt and pepper, flour, Parmesan cheese and chopped basil and combine. Pour egg mixture over vegetables in skillet and make sure mixture covers them. Cook, pushing egg to center to be sure they cook thoroughly.
When eggs are almost set, remove from heat and sprinkle with basil and shredded cheese. Place skillet in oven under broiler and keep a close eye so the cheese doesn't burn.
Remove from skillet by tipping to one side and place on a flat serving plate. Slice tomatoes and place all over the top of the frittata. Cut into wedges and serve immediately. Makes 8 servings. Enjoy!