Preheat oven to 350 degrees F.

In a large bowl add eggs, milk, garlic, salt, pepper, balsamic vinegar, italian seasoning and fresh basil. Whisk until blended.

In a 12" cast iron skill over medium heat, saute onions in olive oil until tender. Add spinach and saute until wilted.

Spinkle cherry tomatoes evenly in skillet, followed by mozzarella balls, and then parmesan.

Carefully pour egg mixture over the top. This is optional, but at this stage you can thinly slice 10 slices of roma tomato and lay on top of frittata for decoration. Continue to cook over medium heat until the sides begin to pull away from the pan. About 6 to 8 minutes.

Place pan in oven on middle rack and bake for 18 to 20 minutes until set. Allow frittata to sit for 5 to 10 minutes before serving.

Slice and garnish with additional cheese, basil, and tomato if desired. Drizzle with olive oil and balsamic vinegar.