Whether you’re looking for an easy, crowd-pleasing brunch dish or a weeknight dinner that doesn’t require a trip to the store, a frittata is always the answer. The Italian egg dish is as simple as it is versatile, and will never let you down. While it’s tempting to fill a frittata with a whole hodgepodge of stuff, keeping things simple lets each ingredient shine. Here, spinach is the star. Its mild flavor is bolstered by sweet shallots, sharp cheddar, and nutty Parmesan. The cheeses melt and mingle with the eggs, giving this dish just the right amount of decadence. Prepping the Spinach This recipe calls for a full 5-ounce clamshell or bag of baby spinach. That might seem like too much for a single frittata, but trust me: Once the spinach wilts down, you’ll have the perfect amount. When you cook the spinach, add it to the skillet one handful …