Directions

1. Preheat the Oven: 

   Begin by preheating your oven to 180℃ (350°F). Lightly grease a large ceramic baking dish with a bit of olive oil or non-stick spray.

2. Prepare the Mushroom-Beef Mixture: 

   In a spacious frying pan, warm the olive oil over medium heat. Once hot, introduce the finely diced onion, carrot, and celery. 

   Sauté until the vegetables turn tender, taking about 2-3 minutes. Incorporate the beef mince into the pan and cook until fully browned. 

   Follow with the diced mushrooms, cooking for an additional 3-4 minutes or until they've softened.

3. Develop the Sauce: 

   Incorporate the tomato paste into the beef and vegetable mixture, ensuring it's uniformly distributed. Introduce the passata and beef stock next. 

   Once the mixture reaches a boil, lower the heat, allowing it to simmer uncovered for approximately 10 minutes. Season with salt and pepper according to preference.

4. Craft the Béchamel Sauce: 

   While the beef-mushroom sauce is developing, direct your attention to the béchamel. In a medium saucepan, melt the butter over moderate heat. 

   Introduce the flour, stirring persistently to avoid lumps, and cook until the roux (butter and flour mixture) starts to foam lightly. 

   Gradually pour in the milk, continuously stirring to ensure a smooth consistency. Keep stirring until the béchamel thickens, becoming reminiscent of a thick cream. 

   Once achieved, remove from the heat and integrate the Dijon mustard and one cup of the grated cheese.

5. Assemble the Lasagne: 

   Initiate the layering by spreading a good amount of the beef and mushroom sauce on the base of your prepped dish. 

   Overlay with lasagne sheets. 

   Smother this layer with a generous portion of béchamel sauce, then lightly sprinkle some of the remaining cheese. 

   Replicate this sequence for 2-3 more layers, ensuring the topmost layer is béchamel generously crowned with cheese.

6. Baking: 

   Cover your lasagne assembly with aluminum foil and usher it into the preheated oven. Bake for 40 minutes. 

   Following this, remove the foil and bake for another 20 minutes. The goal is a bubbly, golden top.

7. Rest and Serve: 

   Once baked to perfection, remove the lasagne from the oven and allow it a 10-minute rest. This settling time aids in more cohesive serving slices. Thereafter, slice into your desired portions and serve piping hot.

   This lasagne radiates perfection when accompanied by a crisp green salad, garlicky bread, or roasted seasonal vegetables. For a wine pairing, consider a refreshing red, such as a Merlot or Pinot Noir.