Spring Green Risotto

Name: Spring Green Risotto
Ingredients: 1 1/2 tablespoons good olive oil; 1 1/2 tablespoons unsalted butter; 3 cups chopped leeks, white and light green parts (2 leeks); 1 cup chopped fennel; 1 1/2 cups Arborio rice; 2/3 cup dry white wine; 4 to 5 cups simmering chicken stock, preferably homemade; 1 pound thin asparagus; 10 ounces frozen peas, defrosted, or 1 1/2 cups shelled fresh peas; 1 tablespoon freshly grated lemon zest (2 lemons); Kosher salt and freshly ground black pepper; 2 tablespoons freshly squeezed lemon juice; 1/3 cup mascarpone cheese, preferably Italian; 1/2 cup freshly grated Parmesan, plus extra for serving; 3 tablespoons minced fresh chives, plus extra for serving