Step 1: Preheat your oven to 375°F (190°C). Prepare a small baking dish or oven-safe skillet. This is one of the easiest vidalia onion recipes, so set yourself up for success!
Step 2: Peel the Vidalia onions and cut them in half lengthwise. Place the onion halves cut-side up in the prepared baking dish. With a sharp knife, score the cut surface of each onion half in a crosshatch pattern, about 1/2 inch deep, being careful not to cut all the way through. This helps the flavors penetrate, a great tip for all vidalia onion recipes.
Step 3: In a small bowl, whisk together the melted butter, olive oil, chopped fresh thyme, chopped fresh rosemary, salt, and black pepper. Generously brush this mixture over the cut surfaces of the Vidalia onions, ensuring the butter and herbs seep into the scored cuts.
Step 4: Pour the chicken or vegetable broth around the base of the onions in the baking dish. Cover the dish tightly with aluminum foil.
Step 5: Bake for 30 minutes. Remove the foil, then sprinkle the grated Gruyère and Parmesan cheese evenly over the top of each onion half. Return the dish to the oven, uncovered, and continue baking for another 15-20 minutes, or until the onions are very tender and the cheese is melted, bubbly, and golden brown. This is where many vidalia onion recipes get their signature golden crust.
Step 6: Carefully remove the baking dish from the oven. Let the baked Vidalia onions rest for 5 minutes before serving. The aroma will be incredible, making this one of the most delightful vidalia onion recipes you'll ever try!