1Heat 2 tablespoons of the oil in a large wide pot or Dutch oven over medium-high heat until shimmering. Add the radicchio, garlic, and a pinch of salt and cook, stirring occasionally, until the radicchio is wilted, about 1 minute. Add the water and cook until it has evaporated and the radicchio is tender, about 2 minutes more. Add the lemon juice and stir to combine. Taste and season with more salt and pepper as needed. Transfer to a medium heatproof bowl; set aside. Wipe out the pot with a paper towel and set it aside.
2Place the broth in a medium saucepan over low heat and keep it at a very low simmer. If you’re using dried mushrooms, place the mushrooms and the 2 quarts of water in a medium saucepan over medium heat and bring to a simmer. Remove from heat and let sit for at least 15 minutes. Strain the mushroom broth through a fine-mesh strainer set over another medium saucepan, leaving any sediment behind, and keep at a bare simmer over low heat. (Either save the rehydrated mushrooms for another use, or chop them, season them with salt, and add them to the risotto halfway through the cooking.)
3In the same large pot or Dutch oven that you used earlier, heat the remaining 1/4 cup oil over medium heat until shimmering. Add the onion and a large pinch each of salt and pepper and cook, stirring often, until the onion is translucent, about 5 minutes.
4Add the rice and cook, stirring, until the kernels start to crackle, about 1 to 2 minutes. Stir in the wine and let simmer, stirring often, until all of the liquid has been absorbed, about 2 to 4 minutes. Pour a ladleful of the simmering broth over the rice. Let simmer, stirring constantly, until the rice absorbs the liquid. Continue adding the broth, stirring and letting it absorb, until the rice is al dente, about 20 to 30 minutes (you may not use up all of the broth). Taste as you go for doneness, seasoning with salt and pepper as needed.
5When the rice is done, remove from heat, add the reserved radicchio, and stir to combine. Add the Parmesan and parsley and stir to combine. Taste and season with more salt, pepper, Parmesan, and lemon juice as needed. Just before serving, loosen the risotto to the desired consistency with a little more broth or hot water and serve immediately. Drizzle each serving with olive oil.