Creamy Buckwheat Pasta with Wild Mushrooms

Name: Creamy Buckwheat Pasta with Wild Mushrooms
Ingredients: 1/2 pound wild mushrooms, such as oysters and chanterelles, sliced 1/4 inch thick; 2 tablespoons extra-virgin olive oil; Salt and freshly ground pepper; 6 large eggs; 1 pound buckwheat pappardelle (see Note); 1 leek, white and light green parts only, halved and sliced 1/8 inch thick; 1/4 cup plus 2 tablespoons mascarpone cheese; 1/4 cup heavy cream; 3 tablespoons unsalted butter; 1 1/2 cups baby spinach; Freshly grated Parmigiano-Reggiano cheese, for sprinkling