Makes 6 servings
By using a slow cooker to make lasagna, you don’t have to boil dried lasagna noodles—and you don’t have to resort to no-boil noodles which can end up gummy and unappetizing. The trick here is to break the dried pasta to fit the shape of your slow cooker (whether round or oval), making even layers of pasta as you build the lasagna.
2 tablespoons olive oil
1½ pounds bulk sweet Italian sausage (that is, the meat without any casings)
3 cups packed baby arugula leaves, chopped
½ teaspoon table salt
3 tablespoons unsalted butter
3 tablespoons all-purpose flour
3 cups whole, low-fat, or fat-free milk
1½ cups finely grated Parmigiano-Reggiano (about 3 ounces)
2 large egg yolks, well beaten in a small bowl
Up to ½ teaspoon grated nutmeg
4 cups (1 quart) plain marinara sauce, store-bought or homemade (here)
1 pound uncooked dried lasagna noodles
1. Heat the oil in a large skillet set over medium heat. Add the sausage and brown well, stirring occasionally, about 5 minutes.
2. Drain the grease. Add the arugula and salt to the skillet and stir over the heat until wilted, just a few seconds. Set aside.
3. In a large saucepan, melt the butter over medium-low heat, then whisk in the flour until the mixture forms a thick paste. Cook, whisking constantly, for no more than 30 seconds, just to get rid of the raw flour taste. Do not allow the mixture to brown. Whisk in the milk in a slow, steady stream and continue cooking, whisking almost constantly, until the mixture bubbles and thickens, 3 to 4 minutes.
4. Remove from the heat and whisk in 1 cup of the Parmigiano-Reggiano along with the egg yolks and nutmeg. Continue whisking until smooth, then set aside.
5. Spoon a thin layer of marinara sauce into the bottom of a 5- to 6-quart slow cooker. Cover the sauce with about a third of the noodles, breaking them to fit and patching them together in one layer. Spoon a third of the remaining marinara sauce over the noodles, sprinkle a third of the meat over the sauce, and top with a third of the cheese sauce.
6. Make two more layers of noodles, marinara, meat, and cheese. Sprinkle the remaining ½ cup Parmigiano-Reggiano evenly over the top.
7. Cover and cook on low for 4 hours. The lasagna can be kept on the machine’s keep-warm setting for up to 2 hours.