Cut the leeks in half lengthwise, then into 4 cm pieces. Slice the carrots, sweet potatoes, and pumpkin thinly. Place all vegetables in a large roasting pan.

Slice the garlic and add it to the pan. Drizzle with olive oil, season with salt, pepper, and a little fresh thyme, then toss to coat evenly.

Roast in a preheated oven at 180°C (350°F), fan-assisted, for 40 minutes, until tender and caramelized. Stir occasionally with a spoon to coat the vegetables in their juices.

In a non-stick pan, sauté the chopped bacon for a few minutes until evenly browned. Transfer to paper towels to drain.

In a small saucepan over medium heat, melt the butter. Add the flour and whisk for 1–2 minutes to cook it lightly. Remove from heat.

Gradually whisk in a little warm milk to dissolve the flour completely, then slowly add the remaining milk, stirring continuously.

Return the saucepan to low heat and cook until slightly thickened, whisking frequently. Season with salt, pepper, and freshly grated nutmeg.

Remove from heat and let rest for 5 minutes. Stir in the cream cheese, egg yolks, and ¾ of the Parmesan until smooth and creamy.

Grease a baking dish. Spread a ladleful of cream sauce on the bottom and layer 4 lasagna sheets.

Add a layer of roasted vegetables, a sprinkle of graviera, and some bacon. Repeat layers three times, finishing with a thick layer of cream sauce. Sprinkle with the remaining Parmesan.

Cover with parchment paper and foil. Bake in a preheated oven at 180°C (350°F) for 35 minutes.

Remove the cover and bake for an additional 10 minutes, until the top is golden and slightly crisp.

Let rest for 15 minutes before serving.