Tennessee Onion Casserole

Get ready to fall head-over-heels for the most incredible side dish that’s about to steal the spotlight at every gathering!

This Tennessee Onion Casserole transforms humble sweet onions into something absolutely magical – we’re talking caramelized, cheesy, herb-kissed perfection that’ll have everyone asking for the recipe.

The secret is in the double cheese combo of mild cheddar and smoky Gouda that creates this incredible melty blanket over perfectly seasoned onions.

Every bite delivers sweet, savory, and just a tiny kick of heat that makes your taste buds do a happy dance.

Trust me, this is comfort food at its absolute finest.

Ingredients

• Active Time: 10 mins
• Total Time: 1 hr 20 mins
• Servings: 10

• Cooking spray
• 2 1/2 lb. sweet onions (about 3 large onions), sliced crosswise into 1/4-in.-thick slices and separated into rings
• 1 tsp. dried thyme
• 1 tsp. dried parsley flakes
• 1 tsp. garlic salt
• 1/2 tsp. dried oregano
• 1/2 tsp. dry mustard
• 1/4 tsp. cayenne pepper
• 1/4 cup salted butter, cut into 1/4-in.-thick pieces
• 4 oz. mild Cheddar cheese, shredded (about 1 cup)
• 4 oz. smoked Gouda cheese, shredded (about 1 cup)

Steps

1. Warm the oven: Preheat oven to 350°F (175°C). Coat a 13- x 9-inch baking dish with cooking spray, making sure to get the corners and sides well-covered to prevent sticking. The generous coating will also help with easy cleanup later.
2. Season the onions: Place onions in a large mixing bowl – you’ll want plenty of room to toss without spilling. Sprinkle with thyme, parsley, garlic salt, oregano, mustard, and cayenne pepper. Toss gently with clean hands or a large spoon to coat evenly. Make sure every onion ring gets kissed with seasoning – this is where all the flavor magic starts.
3. Add to baking dish: Arrange the seasoned onions evenly in your prepared baking dish. Don’t worry about making it perfectly neat – rustic is beautiful here. Just aim for an even layer so everything cooks at the same rate.
4. Add toppings and bake: Arrange the butter pieces evenly over the onions, distributing them so each area gets some richness. Sprinkle the Cheddar and Gouda cheeses over the top, creating an even blanket of melty goodness. Cover tightly with aluminum foil – this traps steam to help the onions get perfectly tender. Bake in preheated oven until onions are soft and you can see the sides bubbling through the foil, about 40 minutes.
5. Finish baking: Remove the foil carefully (watch out for that hot steam!). Continue baking at 350°F (175°C) until the top is golden brown and irresistibly bubbly, about 30 more minutes. The cheese should be beautifully caramelized with some darker golden spots – that’s where the best flavor lives.

Smart Swaps

• Vidalia onions instead of sweet onions (1:1 ratio) – even more natural sweetness
• Sharp cheddar for mild cheddar – adds more tangy bite
• Fresh herbs instead of dried (triple the amount) – use 3 tsp fresh thyme and parsley

Make It Diabetes-Friendly

• Reduce butter to 2 tablespoons – saves 8g carbs per serving while maintaining richness
• Use reduced-fat cheeses – cuts 2-3g carbs per serving without sacrificing flavor
• Serve smaller portions (1/12 instead of 1/10) – reduces carbs from 12g to 10g per serving
• Pair with lean protein like grilled chicken to slow glucose absorption
• Add fiber by serving alongside a green salad to further moderate blood sugar impact
• Total carb reduction: approximately 4-5g per serving with modifications

Pro Tips

• Slice onions uniformly for even cooking – a mandoline slicer works perfectly
• Let casserole rest 5-10 minutes before serving – helps set the cheese and prevents burns