For the meat mixture: In a heavy-bottomed pan, heat the olive oil. Add the celery, carrots, onions, and rosemary and season with a little salt and pepper. Stir, then cook for about 5 minutes.
Add the ground beef and cook, stirring often, until thoroughly cooked, about 15 minutes.
Add the red wine and cook about 10 minutes. Lower the heat to medium, then add the tomatoes and simmer for 1 hour, stirring occasionally. Check the seasoning. Set aside and let it cool.
For the bechamel: Heat the milk in a small saucepan, but keep it from boiling. In another deep saucepan, melt the butter over medium heat. Add the flour, salt and nutmeg and whisk until smooth and light gold. Add the heated milk, 1 cup at a time, whisking constantly. Cook, constantly whisking, until it thickens, for another 10 minutes. Set aside and let it cool.
For the lasagna layers: Bring a large pot of salted water to the boil. Set up an ice bath and set aside. Preheat the oven to 375 degrees F. Generously butter a 12-by-20-by-2 1/2-inch baking dish.
Drop the lasagna sheets in the boiling water a few at a time, then cook for 1 minute. Transfer the lasagna sheets to the ice bath, then drain and lay the pasta flat.
To the prepared baking dish, add a layer of lasagna sheets, a layer of bechamel, a layer of freshly grated Parmesan and a layer of meat sauce. Repeat twice, using all the ingredients.
Bake until golden brown and bubbling, about 30 minutes. Allow to rest for 5 minutes prior to slicing and serving.