Side dish / Vegetarian entrée
A comforting Italian side dish featuring tender, butter-braised leeks enveloped in a velvety béchamel sauce. Finished with a savory crust of Parmigiano-Reggiano, Gruyère, and toasted breadcrumbs, this gratin offers a sophisticated balance of sweetness and rich, nutty flavors.
Recipe video
Begin by preparing the leeks. Trim off the dark green tops and the roots. Carefully slice the white and light green stalks into rounds approximately 1.5 cm (1/2 inch) thick. It is important to treat these gently to keep the rings intact.
Place the sliced leek rounds into a large basin of cold water. Swish them around thoroughly with your hands to loosen any hidden soil or grit between the layers. Lift the leeks out into a colander, drain the water, and pat them dry with a clean kitchen towel.
In a large skillet or wide pan, melt the first portion of butter (30g) together with the olive oil over a steady medium heat. The oil prevents the butter from burning while providing a richer flavor base.
Add the cleaned leeks to the skillet along with the salt and pepper. Stir gently to coat them in the fats. Cover the pan with a lid and cook for about 8 to 10 minutes. You want them to become very tender and translucent without taking on any brown color.
While the leeks are softening, start the Béchamel. In a medium saucepan, melt the 40g of butter over medium-low heat. Once bubbling, whisk in the flour all at once to create a roux. Cook this paste for 2 minutes, whisking constantly, to remove the raw flour taste.
Gradually pour the warm milk into the roux in small increments. Whisk vigorously after each addition to ensure a smooth, lump-free consistency. Continue cooking over medium heat, whisking until the sauce thickens enough to coat the back of a wooden spoon.
Remove the sauce from the heat and stir in the ground nutmeg and a pinch of salt. Taste it to ensure it is perfectly seasoned. Set this aside while you prepare the baking dish.
Preheat your oven to 200°C (400°F). Lightly grease a 23x23 cm (9x9 inch) baking dish with a little butter. Spread the braised leeks into an even, flat layer at the bottom of the dish.
Pour the warm Béchamel sauce evenly over the top of the leeks, using a spatula to spread it into all the corners so every piece of leek is covered in the velvety sauce.
In a small bowl, combine the grated Parmigiano-Reggiano, shredded Gruyère, and coarse breadcrumbs. Add the fresh thyme if using, and toss well to ensure the cheese and crumbs are evenly mixed.
Sprinkle the cheese and breadcrumb mixture in a generous, uniform layer over the sauce. This will form the flavorful, crunchy crust that characterizes a classic gratin.
Transfer the dish to the middle rack of your preheated oven. Bake for 20 to 25 minutes. Watch for the sauce to start bubbling at the edges and the top to turn a deep, appetizing golden brown.
Once finished, remove the gratin from the oven. Allow it to rest for at least 5 minutes before serving. This short wait allows the sauce to set slightly, making it much easier to portion and serve beautifully.
Type of dish: Side Dish / Vegetarian Entrée
