In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add 1 chopped onion, 2 minced garlic cloves, 1 diced carrot, and 1 diced celery stalk; sauté for about 10 minutes until the vegetables soften.

Next, add 500g of ground meat and cook until browned. Stir in 400g of tomato puree, 400g of canned diced tomatoes, and season with oregano, basil, paprika, nutmeg, salt, and pepper. Let it simmer on low for 30 minutes, stirring occasionally.

Bring a large pot of salted water to a boil. Add the pre-cooked lasagne sheets and cook for 2-3 minutes until they are slightly tender but not fully cooked. Drain and lay them flat on a clean surface.

In a saucepan, melt 50g of butter over medium heat. Add 50g of flour, whisking continuously to create a roux for about 2 minutes until golden. Gradually pour in 500ml of milk while whisking to avoid lumps. Continue stirring until the béchamel thickens, approximately 15 minutes.

In a greased baking dish, spread a thin layer of béchamel sauce at the bottom. Layer 3-4 lasagne sheets over the sauce, followed by half of the meat sauce. Sprinkle a generous amount of cheese on top and repeat the layering, ending with béchamel sauce and a final layer of cheese.

Preheat your oven to 180°C (356°F) and cover the lasagne with aluminum foil. Bake for 25 minutes covered, then remove the foil and bake for an additional 20 minutes, or until the top is bubbly and golden brown.

Once baked, let it rest for at least 20 minutes. This allows the layers to set and makes it easier to slice.