Onion and Parmesan Risotto

1/2 cup unsalted butter
8 cups chicken broth
1 medium Texas 1015 or other sweet onion, finely chopped
2 cups Italian arborio rice
1/2 cup white wine
kosher salt to taste
freshly ground black pepper to taste
1 tablespoon lemon zest
1/2 cup Reggiano Parmesan cheese (grated)

In a heavy saucepan heat half the butter over medium-low heat. Meanwhile, in a separate pan, heat the chicken broth. Sauté onion until golden brown, about 15 minutes. Add rice and cook for 2 minutes. Add white wine and cook until absorbed. Turn heat up to medium and set timer for 15 minutes. Add hot broth a cup at a time, stirring carefully until each cup is absorbed. Season to taste with salt and pepper. After timer sounds, stir in remaining butter, lemon zest, and grated cheese.