Risotto is always on our menu, but it changes depending on what's in season. You could serve this Spring risotto with chicken or fish but even alone, as a light supper, it will make your guests happy.
Pour the stock into a saucepan, place over high heat, and bring to a boil. Meanwhile, snap off the ends from the asparagus and peel any tough skin from the stalks. Add the asparagus ends to the stock, reduce the heat to low, and simmer gently until the stems are tender, about 7 minutes. Dip out and discard the stems. Slice the spears 1/4 inch thick on the diagonal. Set aside.
Heat the olive oil in a heavy medium saucepan over medium-high heat until hot. Scatter in the mushrooms and do not move them until they begin to brown, about 1 minute. Then season with salt and pepper, and sauté until brown, about 5 minutes. Remove to a plate.
Lower the heat to medium, add the onion, season lightly with salt, and cook until soft but not brown, about 2 minutes. Add the garlic and cook briefly. Add the rice and stir until the grains look pearly white, about 2 minutes.
Add the wine, if using, and cook until the pan is nearly dry. Adjust the heat so the rice cooks at a slow simmer. Ladle 1/2 cup of the stock into the pan, stir, and cook until the pan is nearly dry again. Season lightly with salt and pepper now so the flavor permeates the rice. Add another 1/2 cup of the stock and continue to stir and cook, adding stock as necessary, until the rice is three-fourths cooked, about 15 minutes. Stir in the thyme, mushrooms, and sliced asparagus tips. Continue to cook until the rice is al dente and the asparagus is bright green and just tender, about 4 minutes longer.
Remove from the heat and stir in the butter, Fontina cheese, 1/2 cup of the Parmesan cheese, the parsley and the lemon zest, if using. Taste for seasoning. Dust with Parmesan before serving. Pass more cheese at the table.
Chef's note: Wwen you want a very fine grating of lemon zest of Parmesan, try using a microplan grater.
