1Heat oven to 450°F. In 12-inch ovenproof skillet, heat oil over medium heat. Crush garlic cloves, leaving them mostly whole; add in skillet. Cook 2 minutes or until garlic begins to brown. Remove from skillet; discard garlic.
2In same skillet, place onion, potatoes, rosemary and thyme. Season with salt and pepper. Cook about 12 minutes or until onion is softened and potatoes are almost thoroughly cooked. Stir in prosciutto.
3In medium bowl, beat eggs and milk with whisk until well blended. Season with additional salt and pepper. Add egg mixture to skillet; slowly move egg mixture around skillet. Transfer skillet to oven.
4Bake 10 to 12 minutes or until puffy and beginning to brown. Remove from oven; sprinkle cheese over top. Return to oven until cheese is melted. Cut frittata into wedges and serve.