Spray a 7x3 oven-safe pan well with cooking spray or grease well with butter.
Whisk together eggs with cream and salt and pepper until well combined. Stir in onions, spinach, and cheese.
Pour the egg mixture into the prepared baking dish. Cover with foil.
Pour in 2 cups of cold water to the inner pot and place the cooking rack inside the inner pot of the Instant Pot. Carefully place the baking dish on the cooking rack. Close the Instant Pot and be sure the vent knob is sealed.
Set to High Pressure and cook for 6 minutes. (Press Manual or Pressure Cook and then use +/- buttons to adjust the time.)
Once the cook time has elapsed, let the pressure release naturally for 10 minutes, before doing a quick release of pressure. Remove the pan carefully from Instant Pot.
Serve warm or at room temperature.
For this Instant Pot Frittata, about 1.5 cups of eggs are needed. That is the equivalent of 6 whole eggs or 12 egg whites. For the dairy, use nonflavored nondairy milk or regular milk or cream. Additional Flavor Combinations
Ham and Cheese: Mix in 1/2 cup shredded cheddar cheese and 1/2 cup diced ham to the egg mixture. and decrease the salt to 1/4 teaspoon.
Vegetable: Add in 1/2 cup of sauteed vegetables to the egg mixture. Mushrooms, peppers, asparagus, broccoli, zucchini, and onions are great additions. I would also suggest adding in 1/4 cup of your favorite cheese.
3 Cheese: Add in 1/2 shredded Fotina cheese. 1/4 cup Parmesan Cheese, and in 1/2 cup cottage cheese.