In a saucepan, bring the broth and 4 cups water to a boil, cover and keep at a simmer.
In a large saucepan, melt 2 tablespoons butter over medium heat. Add the onion and cook, stirring, until softened, about 5 minutes. Add the rice and stir until lightly toasted, about 2 minutes.
Stir in 1 cup of the broth mixture, bring to a simmer and cook, stirring, until the liquid is absorbed, 2 to 3 minutes. Maintaining a low simmer, continue to add the broth mixture, 1/2 cup at a time, stirring frequently and allowing the rice to absorb the liquid. Cook until the rice is tender, about 20 minutes.
In the last 3 minutes of cooking, add the artichoke hearts, lemon peel, lemon juice and the remaining 2 tablespoons butter; season with salt and pepper. Stir in the cheese, parsley and walnuts.
