“Frittata” must be Italian for “kitchen sink.”

And so we find another recipe fit for these straitened times, using up all the tasty bits leftover in the refrigerator, bound together by the always-appealing yet easily-gotten egg.

For such a basic recipe, frittata directions abound yet, to my mind, some are obligatory.

Always add some sort of whole-fat dairy such as whole milk (either as straight milk or whole-milk Greek yogurt), crème fraîche, whipping cream, Mexican crema, sour cream, or even buttermilk. It “custardizes” what might otherwise become a dried-out omelet. In a pinch, 2  percent milk works, but it’s really more like just adding water.

The milk-to-egg ratio is important. For every 6 eggs, use at least 1/4 cup dairy. The cheese, if used, doesn’t count here; it’s in addition to the whole milk and it’s generous.

For every 6 eggs, use up to 1 full cup of grated cheese. Drier or firmer cheeses such as Parmigiano-Reggiano or Gruyère go on top generously; wetter cheeses such as ricotta or goat’s cheese go inside minimally.

The other ingredients, whether leftovers or raw-to-start, need to be fully cooked and at room temperature before assembling the frittata. An easy go-to measure is 2 cups of add-in ingredients (leftovers, cooked vegetables, pasta, rice or other grain, chopped meat or bacon, and the like) for every 6 eggs.

Many frittata flavorings or additions, such as mushrooms, tomatoes, squashes, greens, sausage filling, aromatics (especially onions) and potatoes contain enough moisture to waterlog and spoil the frittata if that wetness isn’t cooked and evaporated out of them before the eggs go in.

The correct pan matters. The best skillet to use is of well-seasoned cast iron because it serves both to begin the frittata on top of the stove (the “frittata,” or “frying” section) as well as stand the heat of the oven in order to finish the frittata.