How to Make It
Preheat the oven to 400°. On a nonstick baking sheet, toss the mushrooms with 1 tablespoon of the olive oil and season with salt and pepper. Roast for 15 minutes.
Meanwhile, in a medium pot of boiling salted water, cook the eggs for 5 minutes. Drain the eggs and cool under cold running water. In another pot of boiling salted water, cook the pasta until al dente; drain well.
In a medium skillet, heat the remaining 1 tablespoon of olive oil. Add the leek and cook over moderate heat until translucent, 3 minutes. Reduce the heat to low and stir in the mascarpone and cream, then stir in the butter. Season with salt and pepper and remove from the heat.
Add the roasted mushrooms, cooked pasta and spinach to the skillet and toss to coat. Season with salt and pepper and mound the pasta into shallow bowls. Peel and halve the eggs, adding one to each bowl. Sprinkle the pasta with Parmigiano-Reggiano cheese and serve immediately.
Buckwheat pasta (called pizzoccheri in Italian) is available at specialty and health-food shops.