Classic and simple meat Lasagna
Heat the olive oil in a skillet over medium heat and brown the onion and garlic; cook until tender, about 8-10 minutes. Reserve in a bowl. In the same pan, brown the ground beef. Once evenly brown, put the onion mixture back into the pan and add the tomato paste, tomato sauce and basil. Cover and simmer over very low heat for 1 ½ - 2 hours, stirring occasionally. Season with salt and pepper.
Melt the butter in a saucepan over medium-low heat. Add the flour and whisk. Gradually add the milk, still whisking, until thick and smooth. Remove from heat, add bay leaf, salt and pepper and set aside.
Preheat the oven to 350 ° F (175 ° C).
Cover the bottom of a 13 x 9-inch dish with a thin layer of meat sauce. Spread a little bechamel over, then cover with grated of mozzarella, then lasagna leaves. Repeat the layers: meat sauce, béchamel, mozzarella, lasagna leaves. Finish by sprinkling Parmesan and what may be left of mozzarella.
Bake 30-40 minutes, until bubbly and top is golden.