Cook lasagna sheets according to package instructions. I recommend cooking your noodles until just slightly harder than you like them. They'll continue to cook in the oven, so it's fine if they're not fully softened. Drain and rinse with cold water to prevent sticking. Set aside.
Add butter, olive oil, and your onion to a large skillet. Place over medium heat and cook until the onions soften and turn translucent (about 3 to 5 minutes). Add the garlic and cook with the onions for another minute or so.
Add your beef to the pan. Brown the beef and break it up while you cook it. If you find there's a lot of liquid in your pan, drain the beef mixture and continue cooking until it browns slightly (about 5 to 10 minutes).
Add basil, oregano, celery salt, sugar, salt, and tomato paste. Cook for another minute or so just to toast and blend everything together. Add your tomato puree and water. Bring the sauce to a boil, reduce heat, and simmer for about 10 minutes (just to thicken the sauce slightly).
To assemble your lasagna, start with a thin layer of meat sauce on the bottom of your baking dish. This helps keep your lasagna noodles from sticking. Lay down 3 to 4 lasagna sheets (depending on the size of your baking dish). Top the noodles with 1/4 of the meat sauce. Continue layering by alternating between 3 to 4 lasagna sheets and 1/4 of the sauce. Complete the layering process with a top layer of sauce to make sure you're top lasagna sheets don't dry out in the oven. Top lasagna with a healthy amount of mozzarella cheese!
Cover your lasagna with an oven-safe lid or aluminum foil. If using a lid, bake for a slightly shorter amount of time to avoid having your lasagna dry out (more information in the blog post above). Bake in a preheated 350°F oven for 25-30 minutes covered. Uncover and bake for another 10-15 minutes, or until the top is slightly golden.
Cool your lasagna for about 10 minutes to make slicing easier. Serve warm.