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Tennessee Sweet Onion Gratin

A close-up of a rich slice of Tennessee Onions Gratin, showing layered onions baked in cream with a golden brown, crispy topping.
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A rich, baked casserole featuring thinly sliced sweet onions cooked slowly until tender and layered with cheese and cream.

Ingredients

Scale
  • 4 large Tennessee sweet onions, thinly sliced
  • 4 tablespoons unsalted butter
  • 1 teaspoon salt
  • 1/2 teaspoon black pepper
  • 1/4 cup all-purpose flour
  • 2 cups whole milk, warmed
  • 1 cup heavy cream
  • 1/2 teaspoon dried thyme
  • 1/4 teaspoon nutmeg
  • 1 cup shredded Gruyère cheese
  • 1 cup shredded sharp white cheddar cheese
  • 1/2 cup panko breadcrumbs

Instructions

  1. Preheat your oven to 375 degrees Fahrenheit. Grease a 9×13 inch baking dish.
  2. Melt the butter in a large, heavy-bottomed pot or Dutch oven over medium heat.
  3. Add the sliced onions, salt, and pepper. Cook slowly, stirring occasionally, for 25 to 35 minutes until the onions are very soft and lightly caramelized. Do not rush this step; slow cooking brings out the sweetness.
  4. Sprinkle the flour over the cooked onions and stir well for 1 minute.
  5. Gradually whisk in the warm milk until the mixture thickens slightly. Stir in the heavy cream, thyme, and nutmeg. Cook for 2 minutes until the sauce coats the back of a spoon.
  6. Remove the pot from the heat. Stir in 1 1/2 cups of the combined Gruyère and cheddar cheese until melted into the sauce.
  7. Layer half of the onion mixture into the prepared baking dish. Sprinkle with half of the remaining cheese. Top with the remaining onion mixture and the rest of the cheese.
  8. Mix the panko breadcrumbs with 1 tablespoon of melted butter (not listed in main ingredients, assume you have butter available) and sprinkle evenly over the top layer.
  9. Bake for 30 to 35 minutes, or until the gratin is bubbly and the topping is golden brown.
  10. Let the gratin rest for 10 minutes before serving.

Notes

  • Using true Tennessee sweet onions, which are similar to Vidalia types, provides the best flavor for this dish.
  • For a deeper flavor, you can substitute half of the milk with dry white wine in the sauce.
  • This dish pairs well with smoked pork or grilled chicken.

Nutrition

Find it online: https://spoonswirl.com/tennessee-onions-gratin-recipe/