Preheat oven to 350 degrees Fahrenheit. Whisk together the eggs, milk, cream, Parmigiano-Reggiano, salt, and pepper to taste in a Pyrex measuring cup.
Melt the butter in a skillet over medium-high heat. Add the shallots until fragrant and translucent. Add spinach and saute on medium high heat until spinach is heated through (about 5 minutes).
Spray a 12-cup nonstick muffin pan with cooking spray. Spoon a generous tablespoon of the spinach and tomato into each cup and top with 2-3 tablespoons of the egg mixture. Each cup will be about 2/3 full. Bake 20-30 minutes. Using a spoon, turn the frittatas out of the pan and serve immediately with toast (and bacon, fruit, etc.)