PREPARATION:
- Heat oil in medium skillet over medium-high heat. Add onions; cook and stir 6 to 8 minutes until soft and golden. Add tomatoes; cook over medium heat 5 minutes. Remove tomatoes and onions to large bowl with slotted spoon; discard drippings. Cool tomato mixture to room temperature.
- Stir prosciutto, cheese, parsley, marjoram, basil, salt and pepper into cooled tomato mixture. Whisk eggs in small bowl; stir into prosciutto mixture.
- Preheat broiler. Heat butter in large broilerproof skillet over medium heat until melted and bubbly; reduce heat to low. Add egg mixture to skillet, spreading evenly. Cook over low heat 8 to 10 minutes until all but top 1/4 inch of egg mixture is set; shake pan gently to test. Do not stir.
- Place pan under broiler about 4 inches from heat. Broil 1 to 2 minutes until top of egg mixture is set. (Do not brown or frittata will be dry.) Serve hot or at room temperature. Cut into wedges. Garnish with parsley.
