Classic Baked Lasagna Bolognese

Ingredients

• 4 tablespoons unsalted butter, plus more for greasing baking dish
• 4 tablespoons all-purpose flour
• 3 cups whole milk
• Kosher salt and freshly ground black pepper
• Pinch freshly grated nutmeg
• 2 pounds fresh homemade plain egg or spinach pasta or store-bought fresh lasagna noodles, or 2 boxes dry lasagna noodles
• Vegetable oil, for greasing pasta
• 1 1/2 quarts warm ragù bolognese
• 3 ounces Parmigiano-Reggiano cheese

Directions

1. Set a small saucepan over medium-high heat and melt the butter, watching so it doesn't brown. Stir in the flour with a whisk to make a smooth paste. Cook it, stirring, until the flour no longer smells raw, about 1 minute. While whisking the whole time, pour in the milk in a narrow, steady stream; if you prefer, add it a couple of tablespoons at a time, whisking well and scraping into the edges of the pan so the sauce stays smooth. It will tighten up at first, then loosen dramatically once all the milk is in. Keep cooking and stirring until it reaches a simmer and starts to thicken a bit. Turn the heat to low and continue stirring until it barely coats the back of a wooden spoon, about 3 minutes. Add salt and pepper, then whisk in the nutmeg. Should lumps show up, whisk vigorously to smooth them; for stubborn large lumps, use a hand blender or countertop blender. Use the béchamel right away, or lay plastic wrap directly on its surface and hold it warm until you need it. The béchamel may also be cooled, covered, and refrigerated for several days; warm it slowly on the stove or in the microwave before using.
2. For homemade pasta, follow the pasta recipe until the point reached after step 10, when you have long fresh sheets; double the amount so the finished pasta totals 2 pounds. You will have more than the lasagna requires, but that cushion keeps you from coming up short while assembling. Cut the sheets into roughly 8-inch-long rectangles.
3. Bring a pot of salted water to a boil. Cook the pasta, in batches if needed, to al dente; exact timing depends on your noodles, but with store-bought pasta, plan on about 1 minute less than the package says. Lift the sheets out with a spider or mesh strainer and move them straight into a large ice bath to stop the cooking.
4. Drain the pasta thoroughly, then slick each sheet lightly with vegetable oil on both sides so the pieces do not cling together. The cooked sheets can wait for up to 3 hours; for that, spread them on a parchment-lined baking sheet and separate the layers with plastic wrap to keep them from sticking.
5. For no-boil pasta, place the sheets in warm water for 30 minutes so they hydrate partway, then set them on paper towels or kitchen towels to drain.
6. When you're ready to assemble and bake, heat the oven to 375 degrees F (190 degrees C). Butter a 9- by 13-inch baking dish. Spread a thin, level layer of ragù across the bottom, then add lasagna noodles over it. A little overlap is fine; trim sheets that are too large so you do not end up with too much doubled pasta.
7. Cover the pasta with another thin coat of ragù; it should be light enough that the noodles show through here and there. Drizzle a little béchamel over the ragù, then scatter grated Parmigiano-Reggiano on top. Continue building the lasagna the same way, with pasta, ragù, béchamel, and grated cheese, until the dish is filled; you should have about 6 layers. End with pasta on top, spread the remaining béchamel evenly over it, and finish with a generous grating of cheese.
8. Bake until the lasagna is bubbling and the top has browned, about 35 minutes. Set the baking dish on a rimmed baking sheet if you want a little backup against spillovers. Rest for 10 minutes before serving.