In a small saucepan, heat the chicken or vegetable stock over low heat. Keep it warm throughout the cooking process as you will gradually add it to the rice later.
Melt 4 tablespoons of unsalted butter in a large skillet over medium heat. Add the mushrooms and finely minced shallots. Sauté, stirring often, until the mushrooms are tender and the shallots are translucent, about 8 minutes. Stir in the minced garlic, thyme sprigs, kosher salt, and ground black pepper, and cook for another minute until aromatic. Once done, transfer this mushroom mixture to a bowl and set aside.
Add the remaining 4 tablespoons of unsalted butter to the skillet over medium heat. Once melted, add the Arborio rice and stir constantly until the rice is translucent around the edges, about 3–4 minutes. Toasting the rice really adds a nutty depth to the finished risotto.
Pour in the dry white wine and fresh lemon juice. Stir and bring to a simmer. Continue stirring constantly until most of the liquid has been absorbed by the rice, about 5 minutes.
Begin adding the warm stock 1 cup at a time to the rice, stirring constantly and allowing each addition to be mostly absorbed before adding the next. Continue this process until the rice is cooked al dente—tender but still with a bit of bite—about 20 to 25 minutes in total. You may not need to use all the stock.
Return the sautéed mushroom mixture (from Step 2) to the skillet and combine with the rice. Reduce the heat to low. Stir in the heavy cream and grated Parmesan cheese, mixing until the risotto is creamy and well combined, about 5 minutes. I like to use Parmigiano-Reggiano for its nutty, savory flavor.
Divide the finished risotto between bowls. Top each serving with more ground black pepper, extra Parmesan, and a sprinkle of fresh chopped parsley if you like. For a burst of color and freshness, I recommend always adding the parsley.