MAKE THE MEAT SAUCE: Heat the 2 tablespoons olive oil in a large saucepan over medium heat. Add the beef and pork along with ¼ teaspoon salt and cook, stirring and breaking up with a wooden spoon or silicone spatula, until no longer pink, 6 to 7 minutes. Transfer the meat and any juices to a bowl. Return the pot to the stove, 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 pot 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 once in a while, until thickened, 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. Use a sharp chef’s knife to cut off the knobby, hairy outside, following the shape of the celery root. If you have a mandoline, set it to ⅛-inch thickness and slice the celery root into about 12 slices (or use the knife to slice the celery root). Sprinkle the slices very lightly with salt. *If you are not using the celery root slices right away, cover them in water, squeeze a little lemon in the water, and refrigerate. Pat dry before using. **Tip: Shred up any unused celery root and use it like potatoes in hash browns.
BUILD AND BAKE THE LASAGNA: Spoon one third (about 1 ⅓ cups) of the sauce evenly across the bottom of an 8 x 10-inch baking dish. Arrange a layer of celery root on top of the sauce, cutting some of the pieces in half if necessary to fit. Cover with another 1 ⅓ cups sauce, a layer of celery root, then finish with the remaining 1 ⅓ cups sauce and the remaining mozz and Parm. Bake until the cheese is melted and bubbly and the celery root can be pierced with a skewer, 20 to 25 minutes. Crank up the broiler and broil until the cheese browns a bit further, 1 to 3 minutes depending on your broiler. Remove from oven and let rest for 5 minutes before cutting into squares.