Cheesy Tennessee Onion Casserole

Prep Steps

• 8 oz extra sharp cheddar cheese {do:shred}
• 1/2 cup parmesan cheese, freshly {do:grate}
• 1/4 cup butter into small cubes {do:cut}

Season the Onions

Preheat the oven to 350°F. Into an extra-large mixing bowl, slice thinly on a mandoline...

• 3 lbs Vidalia onions, about 3–5 onions

Add to the bowl...

• 1 tbsp olive oil
• 1 tbsp brown sugar
• 1 tsp dried thyme
• 1 tsp paprika
• 1 tsp garlic powder
• 1/2 tsp dry mustard
• 1/2 tsp kosher salt{tip:We test with Morton kosher salt. Using table salt? Use about 3/4 as much. Diamond Crystal? Use about 1 1/2 times as much.}
• 1/4 tsp cayenne pepper
• 1/4 tsp black pepper

Toss, separating the onions into individual rings, until they're evenly coated.

Layer

Have ready for layering with the onions...

• 8 oz extra sharp cheddar cheese, shredded
• 8 oz sliced Swiss cheese

In a 9x13-inch casserole dish, spread half the onions, then top with half the cheddar and half the Swiss.

Repeat with the remaining onions, cheddar and Swiss, then top evenly with...

• 1/2 cup parmesan cheese, freshly grated
• 1/4 cup butter, cut into small cubes

Bake

Cover the dish with foil and bake 45 minutes.

Remove the foil and bake 30 minutes more, until golden brown.

Let rest a few minutes before serving.