Tennessee Onions (Cheesy Baked Onion Casserole)

Prep Time	Cook Time	Total Time
15 min	35 min	50 min

Introduction

This cheesy baked Tennessee onions casserole turns simple sweet Vidalia onions into the most irresistible, melty side dish.

The onions roast low and slow in butter and spices, then get smothered in three kinds of cheese for big comfort-food flavor.

It’s perfect for holiday dinners, potlucks, or any night you want an easy, crowd-pleasing side that steals the spotlight.

Prep mode (keeps screen active)

Preheat oven and prepare baking dish

Set your oven rack to the center position for even browning.
Preheat the oven to 375°F.
Lightly grease a 9x13-inch baking dish with butter or cooking spray.
Slice and arrange the onions

Peel the onions, trim the ends, and slice them into ½-inch thick rounds if not already cut.
Separate the slices into rings, keeping some rounds mostly intact for a pretty presentation.
Spread the onion rings in the baking dish in a snug single layer, overlapping slightly as needed.

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Mix the seasoned butter

In a small bowl, combine the melted butter and vegetable bouillon powder.
Stir in the salt, black pepper, garlic powder, smoked paprika, and fresh thyme leaves.
Taste a tiny dab and adjust the seasoning if you prefer a saltier or smokier casserole.
Assemble the cheesy onion casserole

Drizzle the seasoned butter evenly over the onions, making sure to reach the edges and corners.
In a separate bowl, toss together the cheddar, mozzarella, and Parmesan cheeses.
Sprinkle the cheese mixture evenly over the onions, covering them generously but in a fairly even layer.
Bake until bubbly and golden

Cover the dish tightly with foil and bake for 20 minutes to let the onions soften.
Remove the foil and continue baking for 15 minutes, or until the cheese is browned and bubbling.
Let the casserole rest for 5 to 10 minutes before serving so the cheese sets slightly.

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Replace sharp cheddar cheese with Gruyere or fontina: Swap the sharp cheddar for Gruyere or fontina for a slightly nuttier, more melty finish that still feels cozy.
Replace mozzarella cheese with provolone: Use provolone instead of mozzarella if you want a deeper, smokier flavor with beautiful long cheese pulls.
Replace butter with olive oil: Replace the butter with olive oil for a slightly lighter, more savory casserole that still tastes rich and satisfying.

Choose the right onions: Sweet Vidalia onions caramelize gently in the oven and stay tender, so they give you that classic Tennessee onion flavor.
Keep onion slices even: Aim for ½-inch slices so the onions cook at the same rate and soften without turning mushy.
Use freshly shredded cheese: Grate the cheeses yourself so they melt smoothly, since bagged shredded cheese often contains starches that hinder melting.
Finish under the broiler: If the top is not browned enough, broil for one or two minutes, watching closely to avoid burning.
Let it rest before serving: A short rest helps the cheesy sauce thicken slightly, so serving is tidier and the flavors taste more pronounced.

Can I use regular yellow onions instead of sweet Vidalia onions?: Yes, yellow onions work, but the flavor will be a bit sharper, so you may want to increase the butter slightly.
Why are my onions still crunchy after baking?: Your slices may be thicker than ½ inch, or your oven might run cool, so add 5 to 10 more minutes.
Can I assemble this ahead of time?: You can slice the onions and mix the seasoned butter earlier, but wait to add cheese until just before baking.
How should I store and reheat leftovers?: Cool completely, refrigerate in an airtight container for up to three days, then reheat covered at 350°F until hot and melty.