Make the meat sauce
Heat 2 tablespoons olive oil in a large
sauté pan over medium heat. Add the beef and pork along with ¼ teaspoon salt and cook, stirring and breaking up the meat with a wooden spoon or silicone spatula, until no longer pink, 6–7 minutes. Transfer the meat and any juices to a bowl.
Return the pan to the stove and add another 2 tablespoons olive oil. Add the onions and cook, stirring, until softened, 5 minutes. Add the garlic and another ¼ teaspoon salt and cook, stirring, 2 more minutes. Return the browned meat and juices to the pan along with the remaining ¼ cup olive oil, tomatoes, chili flakes, and ½ teaspoon salt. Bring to a boil, reduce the heat to a low simmer, and cook, stirring occasionally, until thickened, about 45 minutes. Remove from the heat and stir in the basil.
Arrange a rack in the top third of the oven and preheat to 350°F.
Make the “noods”
While the sauce is cooking, prepare the celery root by cutting ½ inch off the top and bottom to create a flat surface. Using a sharp chef’s knife, cut off the knobby outer skin, following the shape of the celery root.
If using a mandoline, set it to ⅛-inch thickness and slice the celery root into about 12 slices (or slice carefully with a knife). Sprinkle the slices very lightly with salt. If not using right away, submerge in water with a squeeze of lemon juice and refrigerate. Pat dry before using.
Tip: Shred any unused celery root and use it like potatoes in hash browns.
Build and bake the lasagna
Spoon one-third of the sauce (about 1⅓ cups) evenly across the bottom of an 8×11-inch
baking dish. Arrange a layer of celery root on top, cutting pieces as needed to fit.
Cover with another 1⅓ cups sauce, another layer of celery root, then finish with the remaining sauce and the mozzarella and Parmesan. Bake until the cheese is melted and bubbly and the celery root is tender when pierced with a skewer, 20–25 minutes.
Increase the oven to broil and broil until the cheese browns slightly, 1–3 minutes depending on your broiler. Remove from the oven and let rest for 5 minutes before cutting into squares.