Savory Mushroom and Herb Steel Cut Oat Risotto

Name: Savory Mushroom and Herb Steel Cut Oat Risotto
Ingredients: 5-1/2 cups vegetable stock (chicken or beef stock may also be used); 2 tablespoons unsalted butter; 1 leek (white and light green part only), halved lengthwise, then cut crosswise into thin slices; 1/2 teaspoon kosher salt; 12 ounces mushrooms (I used a mixture of button, cremini, shitake and oyster mushrooms); 2 garlic cloves, minced; 1 teaspoon chopped fresh thyme leaves; 1 teaspoon ground dried sage; 1/4 cup dry white wine; 1 cup steel cut Irish oatmeal (not the quick-cooking kind); 1/4 cup grated Parmesan cheese, plus extra for garnish; 2 tablespoons chopped fresh parsley, for garnish