This Broccoli, Leek, and Mozzarella Quiche is really easy because it doesn't have a crust. And, to be honest, I think the crust just gets in the way of the flavor to begin with.
Preheat oven to 350° F. Generously butter or spray with non-stick cooking spray, a 10-inch pie dish and coat lightly with breadcrumbs.Set aside.
In a skillet over medium heat, melt 1 tablespoon butter. Add leeks and cook until soft and lightly golden, about 5–7 minutes. Remove cooked leeks from the pan,and spread leeks evenly over the breadcrumbs in the baking dish.
In the same skillet, add broccoli and sauté 2–3 minutes until just tender. (If moisture is released, cook an additional minute to evaporate it.) Spread broccoli over the leeks.
Sprinkle mozzarella and Gruyère evenly over the vegetables.
In a medium bowl, whisk together eggs, milk, salt, and pepper until smooth. Let sit for 5 minutes to reduce air bubbles. Pour custard evenly over filling, place the dish on a rimmed baking sheet, and bake for 35–45 minutes, until the edges are set, the center has a slight jiggle (not liquid), and the top is golden brown.
Let cool 10–15 minutes before slicing. This allows the custard to fully set for clean slices.
Notes
Cover leftovers tightly and keep in the fridge for up to 3 days. Do not let food sit at room temperature for more than 2 hours.