Make the Ragù: Heat olive oil in a large pot over medium heat. Add ground meat and cook until browned, breaking it up with a spoon. Drain excess fat. Add onion and cook until softened, about 5 minutes. Stir in garlic and cook for 1 minute more. If using, pour in red wine and deglaze the pan, scraping up any browned bits. Add crushed tomatoes, beef broth, and oregano. Bring to a simmer, then reduce heat to low, cover, and cook for at least 1 hour, or up to 2 hours, stirring occasionally, until thickened and flavorful. Season with salt and pepper.

Prepare the Béchamel: In a separate saucepan, melt butter over medium heat. Whisk in flour and cook for 1-2 minutes to create a roux. Gradually whisk in the warm milk, ensuring no lumps. Continue whisking constantly until the sauce thickens and comes to a gentle boil. Remove from heat, stir in nutmeg, salt, and pepper to taste.

Cook the Pasta Shells: Cook the jumbo pasta shells according to package directions until al dente. Drain and rinse with cold water to prevent sticking.

Assemble the Stuffed Shells: Preheat oven to 375°F (190°C). Spread a thin layer of béchamel sauce on the bottom of a large baking dish. Carefully fill each cooked pasta shell with a generous spoonful of ragù. Arrange the filled shells in the baking dish.

Bake: Pour the remaining béchamel sauce evenly over the stuffed shells. Sprinkle with grated Parmesan cheese (and mozzarella if using). Bake for 25-30 minutes, or until bubbling and golden brown on top. Let rest for a few minutes before serving.