Finely mince a shallot, zest and juice the lemons, and grate the parmesan. Cube the butter into small chunks and place back in the fridge until later.
In a small pot, heat broth or water over medium heat, with a lid on, until steamy.
In a large pot or pan, heat olive oil over medium heat. Then, add the shallot and sweat until translucent and soft. Add 1 tablespoon of lemon zest and stir to combine until fragrant.
Next, add the arborio rice to the pan and stir until rice is lightly toasted, being sure not to burn onions. Add the sherry wine and use a wooden spoon to deglaze the pan and scrape the "fond" (brown bits) off the bottom.
Once the wine has cooked and absorbed and the rice is almost dry, add a ladle-full of the hot water or broth. Stir continuously until the liquid is absorbed. Then, add another ladle.
Repeat this process until the rice is cooked through.
Once rice is cooked, add the lemon juice, the other tablespoon of lemon zest, parmesan cheese, and the cold cubed butter.
Stir vigorously until the butter and cheese are fully emulsified into the risotto. Add salt and pepper and adjust to your liking.
Serve hot and garnish with fresh chives, flaky salt, and any remaining lemon zest.