Check off each step as you cook.

1. 01Build the meat sauce.Heat the oil in a wide saucepan over medium heat. Cook the onion for 5 minutes, then add the garlic and beef. Cook for 7–8 minutes, breaking up the meat, until browned. Stir in the tomato paste for 1 minute. Add the tomatoes, water, oregano, two-thirds of the measured salt, and pepper. Simmer partly covered for 20 minutes, stirring occasionally, until thick but spoonable. The beef mixture must reach at least 160°F / 71°C.
2. 02Prepare pasta and filling.While the sauce simmers, heat the oven to 375°F / 190°C. Boil the lasagna sheets in salted water until just pliable and slightly firmer than al dente, following the package timing. Drain and lay them separately on a clean tray. In a bowl, mix the ricotta, egg, half the Parmesan, and remaining measured salt.
3. 03Layer the dish.Spread a thin layer of meat sauce in a 9 × 13-inch baking dish. Lay in three pasta sheets. Spread half the ricotta mixture over them, then add one-third of the remaining sauce and one-quarter of the mozzarella. Repeat with three sheets, the remaining ricotta, another third of the sauce, and another quarter of the mozzarella. Finish with the final three sheets, remaining sauce, remaining mozzarella, and remaining Parmesan.
4. 04Bake until bubbling.Cover the dish with foil, tented so it does not rest on the cheese, and set it on a rimmed tray. Bake for 25 minutes. Remove the foil and bake for 15–20 minutes more until the edges bubble, the top is lightly golden, and the center reaches at least 165°F / 74°C.
5. 05Let the layers settle.Rest the lasagna for 15 minutes before cutting into portions. Use a broad spatula to lift each piece, keeping the layers together as much as possible.

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