In medium bowl, beat all ingredients except prosciutto, butter and onion thoroughly with fork or whisk until well mixed.
Stir in prosciutto.
In 10-inch nonstick skillet, melt butter over medium-high heat.
Add onion; cook 4 to 5 minutes, stirring frequently, until crisp-tender.
Reduce heat to medium-low.
Pour egg mixture into skillet.
Cover; cook 9 to 11 minutes or until eggs are set around edge and lightly browned on bottom.
Cut into wedges to serve
Notes & Wine Advice
Healthy twist :To reduce the fat to about 3 grams and calories to about 80 per serving, substitute 2 cups fat-free egg product for the eggs. Substitute cooked turkey ham for the prosciutto.