In a large Dutch oven or saucepan, heat 2 tablespoons of olive oil over a medium-high flame. Sauté the mushrooms until nicely browned and their liquid has been released, about 5 minutes. Add the rosemary and season generously with salt. Cook one minute more. Remove the mushroom mixture to a bowl.
Add the remaining olive oil to the pan and sauté the fennel and leeks over medium heat until soft, about 5 minutes. Add the garlic and cook until fragrant, one minute more. Stir in the rice and toast until the edges are opaque and the center pearly white, about 2 minutes. Add the wine and 1 teaspoon sea salt to the pan, scraping up any brown bits, and cook until reduced by half.
Meanwhile, heat the stock in the microwave or on the stove until warm, but not scalding.
Add 1 cup of the stock to the pan. Bring to a simmer, then turn the heat down to medium low and gently cook until nearly absorbed. Repeat this process, adding stock by ½ cup measures, until the rice is tender, about 25 minutes. You want the risotto to be loose enough that it will spread on a plate, so add more stock as necessary for it’s not gloppy. Stir in the reserved mushrooms and half the chives. Taste for seasoning. Garnish with the remaining chives and serve immediately.