2 ounces (½ stick) unsalted butter, diced, plus more for greasing the baking dish
2 ounces all-purpose flour
1 quart milk
½ small yellow onion
1 bay leaf
Generous pinch freshly grated nutmeg
Freshly ground black pepper
1 recipe Fresh Egg Pasta lasagna
6 cups Ragu Bolognese
6 ounces grated Parmegiano-Reggiano
Heat the butter in a small, heavy saucepan over medium heat until it melts, bubbles, and the foam subsides. Add the flour and cook, whisking constantly, for 2 to 3 minutes, or until it begins to smell toasty. Whisk in the milk. Bring to a boil, whisking constantly, add the onion, bay leaf, clove, and nutmeg, and simmer for 20 to 22 minutes, or until thick. Remove from the heat, strain through a fine mesh sieve, and season to taste with salt and pepper. Let cool.
Cook the lasagna in 5 or 6 batches in a large pot of boiling, salted water for 1 to 2 minutes, or until it begins to soften. When the lasagna begins to soften, using a wire skimmer, transfer it from the pot to a large bowl of ice-cold water to stop the cooking process, and then drain it thoroughly. Layer the lasagna between clean kitchen towels to dry.
Preheat the oven to 375˚F. Butter a deep 9×13-inch baking dish. Spread ¾ cup of the ragu in the bottom of the baking dish. Arrange a single layer of lasagna in the dish, spread evenly with ½ cup of the white sauce and then a heaping ¾ cup of the ragu, and sprinkle evenly with ¼ cup of the Parmegiano. Make more layers with the remaining lasagna, white sauce, ragu, and Parmegiano in the same manner, finishing on a layer of Parmegiano. Bake for 35 to 40 minutes, or until the sauce is bubbling around the edges. Cover with foil to keep warm and allow to rest 20 to 25 minutes before serving.
Serves 8. The lasagna should be boiled until it begins to soften but not until it is al dente. Undercooking the pasta in this way ensures that it doesn't become too mushy once it's baked.