If you’ve ever craved a side dish that’s both unbelievably simple and wildly satisfying, this is it. The Tennessee onion casserole—often called Tennessee onions—layers sweet onions, butter, and a lush blanket of melty cheeses. The result? A pan full of tender onion rounds bubbling under a golden, toasty top that practically asks for a spoon. This is the kind of comforting bake that turns weeknights into events and holidays into traditions. Maillard Reaction, explained.

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What Is Tennessee Onion Casserole?

The classic version is stunningly simple:

Sliced sweet onions (rings or half-moons) arranged in a casserole
Dabs of butter (or a melted drizzle)
A cozy spice blend (typically garlic powder, kosher salt, black pepper; some cooks add paprika, cayenne, or dry mustard)
A cheese duo or trio (cheddar + smoked gouda + Parmesan is a beloved combination)

The onions steam-tender under foil, then finish uncovered so the cheese melts and browns. It’s like the soul of French onion flavors—without the stove-top caramelizing—and with more cheesy, baked-in comfort.

Ingredients for Tennessee Onion Casserole

1) Onions: The Star of the Show

The sweeter the onion, the more luxurious the bake:

Best picks: Vidalia, Walla Walla, or Maui
Slice thickness: Aim for ¼-inch. Thinner slices soften faster; thicker slices keep a touch more structure.
Ring vs. half-moon: Rings are classic for the look; half-moons pack a bit tighter and layer evenly in corners.
Quantity: For a 9×13 pan, plan on 3–4 large sweet onions (about 2–2½ pounds), depending on how generously you layer.

Pro tip: If your onions are particularly juicy, pat them dry with paper towels after slicing to reduce excess moisture in the pan.

2) Butter & Seasoning: The Comfort Layer

Butter adds body and helps the cheeses blanket the onions. For seasoning, keep it balanced:

Base blend: garlic powder, kosher salt, freshly ground black pepper
Boosters (optional): paprika for color, cayenne for gentle heat, dry mustard for brightness
Herb twist: a pinch of dried thyme or Italian seasoning for an aromatic edge

3) Cheese: Choose Melt + Flavor

Think about meltability and flavor pop:

Cheddar (mild or medium): classic melt + familiar flavor
Smoked Gouda: subtle smoke and velvety melt that flatters sweet onions
Parmesan (or Grana Padano): salty, nutty top note that helps browning
Alternates: Havarti (buttery), mozzarella (stretchy), provolone (mild smoke), fontina (silky)

Ratio guide:

1½–2 cups cheddar (shredded)
1–1½ cups smoked Gouda or Havarti (shredded)
¼–½ cup Parmesan (finely grated) for the finish

4) Pan & Tools

Pan: 9×13 casserole dish (ceramic or glass)
Cover: Foil for the first stage of baking
Knife or mandoline: For even ¼-inch slices
Grater: Freshly grated cheese melts more evenly and browns better

Tennessee onion casserole with bubbly cheddar and gouda

The Step-by-Step Method

1) Preheat & Prep

Preheat oven to 350°F (175°C).
Grease a 9×13 casserole dish with butter.
Slice onions into ¼-inch rings or half-moons.

2) Layer the Onions

Scatter a generous layer of onions.
Dot with butter (or drizzle melted butter).
Season with your base blend.
Repeat 2–3 layers until the pan is comfortably full but not mounded.

3) Add Cheese

Sprinkle cheddar and smoked gouda/havarti between layers for fuller flavor.
Finish with a generous blanket of cheddar + a shower of Parmesan.
Optional: a light dusting of paprika for color.

4) Cover & Bake

Cover tightly with foil and bake 25–35 minutes until the onions are tender when pierced.
Remove foil.

5) Brown the Top

Bake uncovered an additional 12–18 minutes, until the cheese is bubbling and lightly browned.
If you want deeper browning, broil for 1–2 minutes, watching constantly.

6) Rest & Serve

Rest 8–10 minutes for the cheese to settle.
Serve warm, straight from the pan.

Doneness cues:

Onion slices are silky-tender, not crunchy
Cheese is fully melted, bubbly around edges
Top is evenly golden with hints of toasty brown

Variations You’ll Actually Make

Cheese Profiles:

“Classic Southern”: medium cheddar + Parmesan
“Smoky Lodge”: smoked gouda + sharp cheddar + a pinch of cayenne
“Silky & Mild”: havarti + mozzarella (kid-friendly, ultra-melty)
“Italianate”: provolone + fontina + dried oregano

Seasoning Twist:

Cajun dusting: 1–2 tsp Cajun seasoning in the spice blend
Paprika-forward: sweet paprika for color + smoked paprika for a faint campfire note
Mustard-bright: ½ tsp dry mustard for lift

Toppings for Crunch (Optional):

Butter-cracker crumbs (Ritz-style) tossed with melted butter and Parmesan
Buttery breadcrumbs (panko works well) plus parsley for color
French-fried onions for a nostalgic crunch on top in the final 8–10 minutes

Allium Medley (for depth):

Combine sweet onions with shallots (silky) or a few red onion slices (color + mild bite).

Make-Ahead, Storing, and Reheating

Make-ahead (up to 24 hours):

Assemble fully through the cheese step.
Cover tightly and refrigerate.
Before baking, let the dish stand at room temp 20–30 minutes (to reduce thermal shock and promote even heating).
Expect to add 5–10 minutes to the covered bake time.

Storing leftovers:

Cool to room temperature, then cover or transfer to airtight containers.
Refrigerate 3–4 days.

Reheating:

Reheat in a 325–350°F oven, covered, until warmed through, then uncover briefly to refresh the top.
Individual portions can be reheated in a skillet with a lid over low heat (the edges re-crisp nicely if you remove the lid for the final minute).

Freezer note: You can freeze, but the texture may soften more than ideal. If freezing, do it unbaked, wrapped well; thaw in the fridge overnight and bake as directed, adding time as needed.

Serving Ideas & Pairings

This gooey pan of Tennessee onions fits almost anywhere:

BBQ mains: pulled pork, smoked brisket, ribs
Steak night: ribeye, strip, or tri-tip
Baked or grilled chicken: herb-butter roasted thighs, spatchcocked chicken
Burgers: scoop warm, cheesy onions as a decadent topper
Holiday table: alongside turkey, ham, prime rib, or a roast

Fresh sides for balance:

Bright slaws (vinegar-based)
Crisp salads with citrusy dressings
Roasted asparagus or green beans for color and snap

Troubleshooting & Pro Tips

“It’s watery.”

Pat onions dry after slicing.
Bake covered long enough to fully soften, then uncover so excess moisture evaporates.
Consider a final 5–7 minutes with the oven door slightly ajar (if safe for your oven model) to reduce steam.

“The top is greasy.”

Use shredded cheese you grate yourself (pre-shredded can include anti-caking agents).
Don’t drown the layers in butter—dot evenly instead.
Let the casserole rest before serving so fats re-distribute.

“The onions are still sharp/crunchy.”

Slices may be too thick or baking time too short under foil.
Add 5–10 minutes covered next time before uncovering.

“Not enough flavor.”

Season between layers, not just on top.
Blend cheddars (mild + medium) and finish with Parmesan for pop.
A pinch of dry mustard or cayenne can brighten the whole pan.

“Uneven browning.”

Spin the pan halfway through the uncovered stage.
For a final touch, broil 1–2 minutes—but watch constantly.

“Cheese didn’t melt smoothly.”

Finely shred, and bring cheeses to room temperature while you prep.
Avoid overheating under the broiler; slow melt first, then quick color.

Frequently Asked Questions

What exactly is Tennessee onion casserole?
A layered bake of sweet onions, butter, seasonings, and cheeses that’s first cooked covered to soften the onions, then finished uncovered to brown the top. Think rustic onion gratin meets classic Southern casserole.

Do I need to caramelize the onions first?
No. The covered stage does the heavy lifting—the onions steam-tender under foil, then the top browns beautifully once uncovered.

What onions work best?
Sweet onions (Vidalia, Walla Walla, Maui) are ideal. If unavailable, choose the mildest yellow onions and slice on the thinner side.

How thick should I slice the onions?
About ¼-inch. Thinner slices soften faster; thicker slices maintain a little bite. Keep the thickness consistent for even cooking.

Which cheeses melt best here?
Cheddar for classic comfort, smoked Gouda for depth, Parmesan for salty-nutty finish. Havarti, fontina, mozzarella, or provolone also work well.