Preheat your oven to 450 degrees Fahrenheit. Take a 1-cup oven-safe baking dish, set it on a rimmed cookie sheet and place it in the oven.
While your oven is heating, prepare the batter. In a medium sized bowl, whisk together one large egg and two egg whites.
Add one tablespoon of grated aged cheese, two teaspoons of whole milk, one teaspoon of salt and a pinch of ground black pepper to the beaten eggs and whisk again thoroughly. Put this mixture aside.
Pour one teaspoon of extra virgin olive oil in small skillet and heat it over medium. When the oil is hot, add minced shallot and cook for a couple of minutes or until softened.
Also add spinach to the skillet and cook for another couple of minutes, until the spinach is wilted.
Season the veggies with salt and pepper and stir into the egg mixture.
Remove the heated baking dish from the oven and generously coat it with cooking spray.
Immediately pour the egg and spinach mixture into the baking dish and top it with one tablespoon of the grated cheese.
Return the dish to the oven and bake for 15 minutes, or until the frittata is puffed up in the centre and golden brown at the top.
Combine salad greens with ¼ teaspoon of cider vinegar and ¾ teaspoon of olive oil. Season the salad with salt and pepper and toss to combine.
Serve your spinach frittata with this salad.