Zucchini Onion Frittata

3 tbsp butter
2 tbsp vegetable oil
2 medium zucchini, sliced thin
1 medium onion, cut in half and sliced
1/2 cup grated parmesan cheese, divided
8 large eggs
1/4 cup milk
1 tsp salt
1/2 tsp pepper
1/4 cup chopped fresh basil

Melt butter with oil in a 12 inch ovenproof skillet over medium heat.
Add zucchini and onion, and saute 12 to 14 minutes or until onion is tender.
Remove from heat and stir in 1/4 cup parmesan cheese.
Whisk together eggs, milk, salt and pepper until well blended.
Pour over begetable mixture.
Bake at 350 degrees for 13 to 15 minutes or until set.
Broil for 1 to 2 minutes until edges are browned.
Sprinkle remaining parmesan cheese and basil over the top and serve warm.