These little gems are perfect for on-the-go. They freeze well. I put them in my freezer in individual baggies and grab a baggie (or 2) to take to work. They are very rich (lots of cheese) - you really don't miss a crust at all. They also look lovely on a brunch table.
Preheat oven to 350 F. Coat 12 standard size muffin cups with cooking spray.
Heat oil in a large skillet over medium-high heat. Cook and stir onion 5 minutes or until tender. Add spinach, pepper, nutmeg and salt; cook and stir over medium heat 3 minutes or until liquid is evaporated. Remove from heat. Stir in bacon; cool.
Combine ricotta, mozzarella and Parmesan cheeses in large bowl. Add eggs; stir until well blended. Add cooled spinach mixture; mix well. Spoon evenly into prepared muffin cups.
Bake 40 minutes or until set. Let stand 10 minutes. Run thin knife around edges to remove from pan. Serve immediately.