In a large mixing bowl, add egg, egg whites, buttermilk, salt, pepper and nutmeg. Mix vigorously with a whisk until fully incorporated and slighlty frothy. Set aside.
Coat a 6" quiche dish with a little bit of olive oil or cooking spray. Add cornmeal and shake pie dish so that cornmeal adheres to all surfaces.
Delicately add butternut squash and rapini then pour egg mixture over vegetables.
Sprinkle cheese and sun dried tomatoes on top and place in the oven, where you will bake the frittata for 25-30 minutes or until completely set and cheese takes a nice golden coloration.