Peel and finely chop the onion and garlic. Rinse the lemon, remove the zest and squeeze the juice into a small bowl.
Melt half of the butter in a large pan. Sauté the onion, garlic and a few pieces of the lemon zest until softened. Add the rice and sauté briefly. Stir in the white wine and 3 tablespoons of lemon juice and cook until the liquid has been absorbed. Lower the heat to medium and stir in a bit of the chicken broth.
Continue stirring in chicken broth, a little at a time, for about 20 minutes, until the rice is al dente and almost all of the liquid has been absorbed.
Stir the remaining butter and grated Parmesan into the rice and season with salt and pepper. Transfer to serving bowls, garnish with shaved Parmesan and lemon zest and serve with a glass of white wine, if desired.