My cheesy Tennessee onion casserole turns a few simple ingredients into a bubbling, deeply savory side dish. Sweet Vidalia onions slowly soften under layers of sharp cheddar and Parmesan, while smoked paprika, mustard, and thyme keep all that cheesy richness from falling flat.
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This is the kind of side dish I pull out when roasted vegetables feel a little too predictable. It works especially well for winter dinners and holiday meals. Think of this as an alternative to a cheesy potato casserole or a creamed corn side dish. The rich, sweet-savory flavors work especially well alongside my trout almondine, herb roasted turkey breast, and BBQ shredded beef.
The basis of this onion side dish is from an old cookbook I have from the 1930's, it was a cheesy baked onion casserole recipe that I jazzed up. During my tasting, one of my testers called it Tennessee onions. I learned it was a whole thing.
📖Why My Recipe Works
- After testing both thinner and thicker slices of onion, I found ¼-inch slices hit the sweet spot. They become tender without disappearing into the cheese.
- The covered baking time traps steam so the onions soften and their natural sweetness develops. Removing the foil lets moisture escape, giving you a cheesy onion bake rather than onions swimming in liquid.
- I tested different cheeses, and sharp cheddar delivered the flavor I wanted at a much more reasonable price point. Parmesan on top adds another savory layer and browns beautifully.
🧾Ingredient Notes
- Onions - I prefer sweet onions in this recipe. If you substitute regular yellow or white onions, add a pinch of brown sugar to the seasoning mixture, but no more than 2 teaspoons.
- Cheddar Cheese - Buy a block and grate it yourself. Pre-shredded cheese contains anti-caking ingredients that keep the shreds separate in the bag but can also prevent the cheese from melting as smoothly. Freshly grated sharp cheddar gives you a creamier, more cohesive layer of melted cheese.
- Parmesan Cheese - Freshly grated Parmesan melts into the cheddar and browns across the surface. Pre-grated Parmesan tends to stay drier and doesn't give the topping quite the same texture.
- Buttermilk or heavy cream - I prefer buttermilk because its acidity adds a little tang that balances the sweet onions and rich cheese. Heavy cream makes the casserole richer and more velvety, so use it if you want a heavier, creamier result.
- Seasonings - Two of my favorite ways to make a cheese-heavy dish more interesting. Mustard powder gives the cheddar a subtle tangy edge, while smoked paprika brings depth without turning this into a spicy onion casserole.
⏲️How to Make Tennessee Onions
- Don't leave the slices as solid onion rounds. Separate them into rings to create spaces for the seasoning, buttermilk, and melted cheese to work their way through the entire casserole.
- For the most classic casserole texture, layer half of the seasoned onions in your prepared baking dish and scatter half of the sharp cheddar over them. Repeat with the remaining onions and cheddar, then finish with Parmesan and small pieces of butter.
- Cover the baking dish tightly with foil and bake for 45 minutes. This first stage is when the onions do most of their softening.
- Remove the foil and bake for another 30 minutes. Now the excess moisture has somewhere to go, while the cheese on top bubbles and browns.
👩🏻🍳Jen's Testing Notes
- Don't slice the onions paper-thin. I tested different thicknesses as well as leaving the slices whole versus breaking them apart. A ¼-inch slice with the rings separated gives you the best texture.
- And about the sugar, one recipe tester was appalled by the version I tested with added sugar. I got the message. More importantly, the recipe didn't need it. Vidalia onions are naturally sweet enough. Sugar and cheese just don't mix in my book.
- Give the onions about 10 minutes to rest before serving. That short wait allows everything to settle instead of sending a flood of molten cheese across your plate.
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📖 Recipe Card
Baked Tennessee Onions
Ingredients
- 1 ½ teaspoons kosher salt
- 1 teaspoon garlic powder
- 1 teaspoon smoked paprika
- 1 teaspoon dried thyme
- ¾ teaspoon dry mustard powder
- ¼ teaspoon cayenne pepper
- 4 large Vidalia onions about 3 pounds peeled and cut into ¼ inch slices
- ¼ cup buttermilk or heavy cream
- 2 cups sharp cheddar cheese shredded
- ½ cup parmesan cheese freshly grated
- 3 Tablespoons unsalted butter cut into small cubes plus more for your baking dish
Instructions
- Preheat the oven to 350 F degrees. Butter a 9x13 baking dish and set aside.
- In a small bowl mix together all the dried spices.1 ½ teaspoons kosher salt, 1 teaspoon garlic powder, 1 teaspoon smoked paprika, 1 teaspoon dried thyme, ¾ teaspoon dry mustard powder, ¼ teaspoon cayenne pepper
- Add the onions and cream to a large mixing bowl. Break up the onion rings and toss with the cream to coat. Sprinkle over the spice mix and toss to evenly distribute the mixture.4 large Vidalia onions, ¼ cup buttermilk
- Place about half the onions in the bottom of the pan, top with half the cheddar.. Repeat with a second layer. Sprinkle over the parmesan cheese. Top with the cubes of butter.2 cups sharp cheddar cheese, ½ cup parmesan cheese, 3 Tablespoons unsalted butter
- Cover with foil and bake for 45 minutes. Uncover and return to the over for an additional 30 minutes or until bubbly and golden brown on top. Cool for 10 minutes before serving. I recommend serving with fresh minced parsley or chives for color.
Notes
- If you use white or yellow onions, add up to 2 teaspoons of brown sugar to the spice mixture.
- Use freshly grated cheese for the best texture.
- Store leftovers covered in the refrigerator for up to 4 days, then reheat in a 350°F oven until hot and bubbly; the microwave works for individual portions, but the oven does a better job of reviving the cheesy top.
Equipment
Nutrition
Common Recipe Questions
"Tennessee onions" is a colloquial term for a cheesy baked onion casserole made with thick slices of sweet onion, butter, seasonings, and plenty of melted cheese. It's typically baked until the onions are tender and the cheese is golden and bubbly.
Onions release a lot of moisture as they cook, so don't skip the uncovered portion of the baking time. The first 45 minutes under foil gives the onions time to soften, while the final 30 minutes uncovered lets that excess moisture evaporate. Also, stick with ¼-inch slices. Thinner onions break down faster and can release their water before the casserole has time to cook it off.
Pat says
It definitely didn't need the sugar. My family liked this version better than the last one I tried.