Description

Tennessee Onions is a comforting, cheesy baked onion casserole featuring thinly sliced Vidalia onions layered with a flavorful spice blend, sharp Cheddar, Swiss, and Parmesan cheeses, then baked to golden perfection. This dish offers silky, tender onions infused with smoky, sweet, and slightly spicy notes, making it a delicious side or vegetarian main.

Ingredients

Scale

Spice Blend

2 teaspoons brown or granulated sugar
1 teaspoon chopped fresh thyme, or 1/2 teaspoon dried thyme, plus more for serving
1 teaspoon smoked paprika
1 teaspoon garlic powder
1/2 teaspoon mustard powder
1/4 teaspoon ground cayenne
Salt and black pepper
1 lemon, zested and halved (optional)

Main Ingredients

3 pounds Vidalia onions (3 to 5 onions, depending on size)
1 tablespoon olive oil
1 cup (4 ounces) shredded sharp Cheddar cheese
1 cup (4 ounces) shredded Swiss cheese
1/3 cup (1 ounce) grated Parmesan cheese
3 tablespoons unsalted butter, cut into small cubes

Instructions

Make the spice blend: Preheat your oven to 350°F (175°C). In a small bowl, mix together brown sugar, fresh or dried thyme, smoked paprika, garlic powder, mustard powder, cayenne pepper, kosher salt, black pepper, and lemon zest if using, creating a well-balanced, aromatic seasoning for the onions.
Prepare the onions: Thinly slice the Vidalia onions crosswise into 1/4-inch rings, separating them into individual rings. Place them in a large bowl and gently toss with olive oil, the prepared spice blend, and juice from half a lemon (if using), ensuring every piece is evenly coated with flavor.
Layer the casserole: Arrange half of the spiced onions in the bottom of a 9×13-inch or 3-quart baking dish. Sprinkle half of the sharp Cheddar and Swiss cheeses over the onions. Repeat layering with the remaining onions, cheeses, and sprinkle the grated Parmesan on top. Dot the surface with small cubes of unsalted butter to add richness.
Bake covered: Cover the dish tightly with aluminum foil to trap moisture. Bake in the preheated oven for 45 minutes until the casserole is bubbling, ensuring the onions become tender and begin melding with the cheeses.
Bake uncovered: Remove the foil and continue baking for another 30 minutes uncovered until the onions are soft and silky and the top has developed a golden-brown, slightly crispy crust.
Finish and serve: Allow the casserole to cool for 10 minutes to set. Sprinkle additional fresh thyme over the top. Serve warm, optionally with lemon wedges for squeezing over the cheesy onions for a bright finish.

Notes

For best results, slice the onions very thinly to ensure they become silky rather than crunchy.
If fresh thyme is unavailable, dried thyme works well; just adjust quantity accordingly.
You can substitute other sweet onions if Vidalia onions are not available, but Vidalias provide the best sweetness.
Leftovers can be refrigerated and gently reheated; the casserole may lose some crispness but remains flavorful.
This dish pairs wonderfully with grilled meats or as a savory vegetarian main served with crusty bread.

Prep Time: 20 minutes
Cook Time: 1 hour 15 minutes
Category: Side Dish
Method: Baking
Cuisine: Southern American

Keywords: Tennessee Onions, baked onions, cheesy onion casserole, Vidalia onion recipe, Southern side dish, cheesy baked vegetables