Preheat oven to 355°F
Heat a non-stick frying pan over medium heat. Add the butter, oil, garlic, and mushrooms and cook for 5 minutes or until mushrooms are golden (add in the parsley after the first few minutes).
Place the rice, stock, and mushroom mixture in an 8.5 x 12 in (10 cup capacity) baking dish and stir to combine. Sprinkle generously with sea salt and freshly cracked pepper. If using, sprinkle with truffle salt. (note: Donna Hay shows her baked risotto with slightly more liquid than I prefer. I have been using 4 cups vs. her recommended 4.5 cups of chicken stock: adjust to your preference. The amount of liquid required will also very based on your add-ins).
Cover tightly with foil and baked for ~40 minutes or until most of the liquid is absorbed. Remove from oven, stir in peas, parmesan and second quantity of butter. Taste and adjust seasonings (you will likely want to add an additional generous amount of sea salt/truffle salt and pepper). Serve immediately.