In a large pot or Dutch oven, heat the olive oil over medium-high heat.

Add the onion and cook until it softens and is translucent, 5-8 minutes. 

Add the garlic and cook until fragrant, another 30-60 seconds. 

Add the celery and carrot along with the salt and pepper and continue to cook until the vegetables are soft, about 10 minutes.

Add the tomatoes, sugar and bay leaf. Reduce the heat to low and simmer uncovered breaking up the tomatoes as the sauce cooks.

Cook until the sauce thickens, about 1 hour. Remove from the heat and discard the bay leaf. 

Cool the sauce slightly, then transfer the sauce to a blender (work in batches, if needed) and process until smooth.

Preheat the oven to 350ºF. Spray a 9x13-inch baking dish with nonstick cooking spray. Spread 3/4 cup of the prepared sauce in the bottom of the dish. Set aside.

Place a skillet over medium heat and add the ground beef and onion. Cook, breaking up the meat as it cooks, until the meat is browned and the onion is soft. Remove from the heat and allow the mixture to cool slightly.

While the beef is cooling, mix the ricotta, one cup of the Mozzarella, 1/4 cup of the Parmesan, the parsley, garlic, salt and pepper in a bowl. When the beef mixture has cooled slightly stir it into the cheese mixture.

Bring a large pot of water to a boil. Salt generously. Add the manicotti and cook until it is softened, but still firm to the bite, about 6 minutes. Remove the manicotti from the water and transfer to a baking sheet to cool off.

Transfer the meat and cheese mixture to a large ziplock bag. Cut off the corner. Squeeze the mixture into the manicotti and place the stuffed pasta in the baking dish in a single layer. Spread the remaining sauce over the top of the pasta. Sprinkle the remaining 1/2 cup of Mozzarella and 1/4 cup of Parmesan over the top. Dot with the butter pieces.

Bake the manicotti, uncovered, until it is heated through and the sauce is bubbling and hot, about 35 minutes.

Let the manicotti sit for 5-10 minutes before serving.