Frittatas are one of our favorite prep-ahead breakfasts because they're simple to make and reheat quite well (we even enjoy them straight out of the fridge or at room temperature). The key to a fluffy frittata is to add a splash of water and whisk your eggs until well combined. We fill this frittata with tender broccoli, fresh shallot and sharp white cheddar cheese for the ultimate way to start your day!