Preheat oven to 375 degrees.
Heat vegetable broth, 1-tablespoon vegetable oil, and 1/4 teaspoon salt in a medium saucepan until it boils.
Place the brown rice in 8X8 baking dish.
Pour the boiling broth mixture over brown rice and give it a gentle stir.
Cover the baking dish tightly with 2 layers of aluminum foil.
Place it in the oven and bake for 60 to 70 minutes or until tender.15 minutes prior to rice being ready,
Sauté leeks in a large skillet with 1-tablespoon oil until they are wilted, 2-3 minutes.
Add the mushrooms and cook, stirring occasionally, until most of the moisture has evaporated, 8-10 minutes.
Season it with 1/4 teaspoon salt, thyme, and black pepper.
When rice is ready, fluff it with a fork and cover it with kitchen towel.
Let it stand for 5 minutes.
Stir in the sautéed mushroom and leek mixture in rice and drizzle it with the sherry vinegar.
Taste for seasoning. Add if necessary.