In a saucepan, bring the broth to a boil. Add the rice; cook for 5 minutes. Drain and transfer to a bowl; return the broth to the pan and keep warm.
In a skillet, heat 2 tablespoons butter over medium-high heat. Add the mushrooms and cook until browned; transfer to a plate.
In a saucepan, melt 1 tablespoon butter over medium heat. Add the shallot and cook until softened. Add the wine and cook until the liquid has evaporated. Stir in the rice, then add the broth, a ladleful at a time, adding more as it absorbs. Cook until the rice is tender, about 10 minutes. Stir in the parmesan, 1 tablespoon butter, the mushrooms and the lemon peel; season with salt. Cover and let sit for 5 minutes.
Meanwhile, in a skillet, heat the remaining 4 tablespoons butter over medium heat. Stir in the sage and cook until the butter turns golden and the sage is crisp, about 5 minutes. Remove the pan from the heat and stir in the lemon juice. Serve the risotto with the toasted butter and sage.