Recipe

1.  Heat oil in a large sauté pan over medium until shimmering. Add onion and season with salt; cook, stirring occasionally, until translucent, about 3 minutes. Fill pan with as much spinach as will fit; cook, stirring, and adding remainder a handful at a time as space allows. When all the spinach is wilted, season with pepper and stir in nutmeg. Drain spinach in a sieve. When cool enough to handle, squeeze excess moisture from spinach by hand.
2. Butter a 3-quart baking dish. Place a third of the bread slices in a single layer in dish. Top with half the spinach mixture and a third of the cheeses. Repeat layering with a third of the bread, remaining spinach mixture, and a third of the cheeses, then top with remaining bread (reserve remaining third of the cheeses).
3. Whisk together 6 eggs and 2 cups milk, season with salt, and carefully pour over bread. Cover with parchment, and gently press down with hands until egg mixture soaks through top of bread. Cover parchment with foil, and refrigerate at least 8 hours (and up to 2 days).
4. Preheat oven to 350°F. Meanwhile, remove strata from refrigerator, uncover, and let stand 30 minutes. Whisk together remaining 2 eggs and ⅔ cup milk, and pour over strata, gently pressing between layers of bread with a spoon or spatula to ensure that egg mixture seeps to bottom. Sprinkle with remaining cheeses.
5. Bake until puffed and golden brown in spots, 45 to 50 minutes. Let cool 15 minutes before serving.

TIP: Young fontina has a softer texture than aged varieties and is often labeled as “semi-firm” or “table cheese”; you can find it at cheese shops and specialty grocers. Regular fontina will also work here.