Wash the potatoes thoroughly, peel, and cut them into cubes. Place them in a large pot of boiling salted water and cook until tender. Remove with a slotted spoon and mash them, collecting the puree in a large bowl.

In the same pot of boiling water, blanch the Tuscan kale leaves (with the tough stems removed and cut into strips) for 5 minutes. Drain, reserving a small glass of the cooking water. Place the kale in a blender or use an immersion blender to puree until smooth, adding a little of the reserved water if needed.

In a nonstick skillet, heat the olive oil and sauté the finely chopped onion. Add the mashed potatoes, pureed kale, butter, and enough milk to create a smooth, creamy mixture. Cook over medium heat until slightly thickened.

Once you have a creamy purée, season with salt and set aside.

Remove the casings from the sausages, cut them into rounds or chunks, and brown them in a nonstick skillet without adding extra fat. Cook until well done and lightly golden. Drain off any excess fat and set aside.

Meanwhile, cook the lasagna noodles in salted water. As they are ready, lay them out on a clean kitchen towel to dry.

In a large bowl, combine the kale purée, lightly beaten eggs, fresh ricotta, grated Parmesan, and cooked sausage. Mix well until fully combined.

Grease a baking dish with extra virgin olive oil and sprinkle with breadcrumbs. Assemble the lasagna by alternating layers of pasta and filling. Finish with a layer of pasta, sprinkle with more breadcrumbs, and drizzle with a little extra virgin olive oil.

Bake in a preheated oven at 375°F (190°C) for 30-40 minutes, until the top is golden and crisp.

Serve immediately.