If using dried lasagna noodles: soak the 8 ounces of noodles in warm water for about an hour; drain and lay them flat or pat dry before assembling. If using no‑boil lasagna noodles, skip soaking.

Heat 2 tablespoons olive oil in a large saucepan over medium heat. Add 1 cup chopped onion and sauté until translucent, about 5–7 minutes. Add 2 cloves minced garlic and sauté until fragrant, about 30 seconds to 1 minute.

Stir in the 28‑ounce can crushed tomatoes, 16‑ounce can diced tomatoes, 6‑ounce can tomato paste, 1 tablespoon brown sugar, 1 teaspoon salt, 1 ½ teaspoons oregano, ¼ teaspoon thyme, 1 bay leaf, the 1 stalk of celery (cut in half), and 2 cups water. Bring to a simmer.

Reduce heat to low and simmer the sauce, partially covered, for 2–3 hours, stirring occasionally. Near the end of the simmer, remove and discard the celery pieces and the bay leaf.

Before adding the sausage to the sauce, spoon out a small amount of sauce (without sausage) and spread it across the bottom of a greased 9 x 13‑inch baking pan to prevent sticking.

Prepare the sausage: if your 4 links Italian sausage (1½–2 pounds) are not already sliced and cooked, slice them and cook in a sauté pan over medium heat until browned and cooked through. If the sausage is already sliced and cooked, simply have it ready.

Add the sliced, cooked sausage to the remaining sauce and stir to combine; simmer a few minutes to meld flavors.

Preheat the oven to 350°F.

Assemble the lasagna in the greased 9 x 13‑inch pan: start with a single layer of noodles covering the bottom (use about half the noodles for the first layer). Spoon and spread about half of the sauce (now containing the sausage) over the noodles. Dollop and spread about half of the 1 pound ricotta cheese over the sauce. Sprinkle about half of the 1 ½ pounds grated mozzarella over the ricotta.

Repeat the layer: remaining noodles, the remaining sauce with sausage, the remaining ricotta, and the remaining mozzarella so you have two noodle layers and two cheese layers.

Cover the assembled pan with a piece of foil that has been lightly greased on the side that will touch the cheese (or use non‑stick foil). Place the covered pan in the preheated oven and bake for 1 hour. If you want more browning on the top, remove the foil for the last 15 minutes of baking.

After baking, remove the lasagna from the oven and let it cool for about 15 minutes before cutting and serving.