For the lemon Parmesan broth: Add the thyme, lemon zest, Parmesan rinds and bay leaf to a medium sauce pan. Cover the mixture with 5 cups water. Place over medium heat and bring to a simmer. Simmer for 20 minutes, skimming the surface as needed. Strain, discarding the solids and reserving the liquid.
For the risotto: Heat a Dutch oven over medium-high heat. Add 2 tablespoons of the olive oil and the shallot and cook until the shallot is soft and fragrant, about 2 minutes. Add the rice and toast, stirring often to coat the rice in the flavored oil, for 2 more minutes. Season with the salt, deglaze with the white wine and cook, stirring often, until the wine is almost entirely absorbed. Add 1 cup of the lemon Parmesan broth and cook, stirring constantly, until the liquid is nearly absorbed. Continue to cook, adding more broth by the cup and stirring often, until the rice is just tender and the mixture is creamy, about 25 minutes total. Finish with the remaining 2 tablespoons olive oil, the chives and grated Parmesan, if using.