• Make the ragù base: In a large skillet or Dutch oven, heat olive oil over medium. Add onion, celery, and carrot; sauté until the vegetables are soft and sweetly scented, about 6–8 minutes.

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• Add garlic and cook 30 seconds more, until fragrant but not browned.
• Increase heat to medium-high. Add ground beef (and pork, if using); break up with a spoon and brown until deeply caramelized on the edges, about 6–8 minutes.
• Pour in red wine; simmer until reduced by half, about 3–4 minutes. Stir in tomato paste and cook 1 minute to bloom the flavors.
• Stir in crushed tomatoes and beef broth. Add oregano (or Italian seasoning), salt, pepper, and a pinch of chili flakes if you like a hint of heat. Simmer gently, uncovered, for 25–40 minutes, until the sauce is rich and thick enough to coat the back of a spoon. If it thickens too much, splash in a little extra broth.
• Meanwhile, make the béchamel: In a small saucepan, melt butter over medium heat. Whisk in flour and cook 1 minute. Slowly whisk in warm milk, continuing to whisk until smooth and thickened, about 4–6 minutes. Season with salt and a pinch of nutmeg. Remove from heat.
• Preheat the oven to 375°F (190°C). If using spinach, wilt it slightly in a separate pan or microwave, then squeeze out excess moisture.
• Assemble: Spread a thin layer of ragù in a 9×13-inch baking dish. Lay down a sheet of pasta, then a thin veil of béchamel, a spoonful of ricotta, some mozzarella, and a sprinkle of Parmesan. If using spinach, add a layer here. Repeat until you’ve used all ingredients, finishing with ragù and a generous topping of mozzarella and Parmesan.
• Bake: Cover tightly with foil and bake for 30–40 minutes, until bubbling and the layers are set. Remove foil and bake another 10 minutes, until the top is golden and bubbly. Let rest at least 15 minutes before slicing to keep its shape. Serve with a bright green salad and crusty bread.