Heat a large cast-iron or saute pan over medium heat. Add the olive oil, leek, onions and a pinch of salt. Cook until tender but not brown, about 5 minutes. Add mushrooms, garlic and thyme and cook, stirring occasionally, for 7 minutes until tender and slightly brown.
Add the rice and cook until the kernels are well coated with the oil and mushrooms, about 2 minutes. Add wine, balsamic vinegar, broth and a pinch each of salt and pepper. Bring the liquid to a boil and then remove from heat. Transfer the mixture to a deep 9x13-inch baking dish. Wrap the top tightly with Reynolds Wrap(R) Aluminum Foil. Bake for 30 minutes until the rice is tender but al dente.
Remove baking dish from oven and add the Parmesan and sage. Stir, adjust seasoning if necessary and serve immediately.