Heat treat the chopped -onion, garlic, celery and bell pepper- on a bit oil over medium heat until it’s collapse.
Shred the minced meet on the vegetables, fry until it’s brown then add the tomato pureé, the ketchup and the mustard. Spice it and when the vegetables just aren’t fresh, it’s ready.
For the bechamel: Start to heat the butter in a saucepan. Add the flour and mix it then gradually add the milk, thicken while it’s heating and finally add the salt and pepper.
Butter the baking sheet, take the bechamel 1/4 then place lasagna noodles on it, on which we take the Sloppy Joe ragout than the grated parmesan. So: bechamel, noodles, ragout, cheese again and at last noodles, bechamel, cheese.
Bake on low-top flame for about 20-30 minutes or until parmesan turns nice brown. If it’s done- let it rest for 10-15 than serve.