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Red Potato and Red Onion Gratin
This Red Potato & Red Onion Gratin is a savory layered bake that combines tender new potatoes with the sweet, mellow bite of red onions, all tied together with thyme and a light buttery finish. It’s a rustic yet refined dish that brings out the natural flavors of its simple ingredients. Baked until golden and slightly crisp at the edges, this gratin is a comforting side dish perfect for family dinners, potlucks, or any meal needing a cozy touch.
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Prep Time 20 minutes
Cook Time 40 minutes
Total Time 1 hour
Course Side Dish
Cuisine American
Servings 6
Calories 221 kcal

Ingredients
  

  • 2 lbs new potatoes (peeled and sliced ¼" thick)
  • 3 tbsp oil (divided)
  • 3 red onions (medium, sliced ¼" thick)
  • ½ tsp thyme
  • 1 tsp salt (divided)
  • ½ tsp pepper (divided)
  • 2 tbsp butter (finely diced)
  • Parsley (for garnish (optional))

Instructions
 

Step 1: Prep Potatoes

  • Place sliced potatoes in a bowl of cold water.
  • Change water 2 or 3 times to remove excess starch.

Step 2: Cook Onions

  • Heat 1 tbsp oil in a skillet over medium heat.
  • Add onions and thyme.
  • Cover and cook, stirring occasionally, for about 10 minutes until onions are wilted but still slightly crunchy.
  • Drain potatoes and pat dry.

Step 3: Assemble Gratin

  • Preheat oven to 425°F.
  • Grease a shallow 2-quart casserole dish with 2 tbsp oil.
  • Arrange half of the potato slices in overlapping circles on the bottom.
  • Season with ⅓ of the salt and pepper.
  • Sprinkle half of the cooked onions over potatoes.
  • Repeat layers, finishing with potatoes.

Step 4: Bake

  • Dot the top with butter.
  • Bake uncovered for 30 minutes, until potatoes are tender and edges are golden.
  • Garnish with chopped parsley, if desired.

Tips

  • Substitute half the red onions with sweet onions for a milder flavor.
  • Add ½ cup shredded Gruyère or cheddar for a cheesy gratin.
  • Mix in a splash of cream for richer texture.
  • Add garlic when sautéing onions for deeper flavor.
  • Try rosemary or sage instead of thyme.
  • Top with breadcrumbs for a crispier finish.
  • Add cooked bacon for a smoky variation.
  • Use purple or Yukon Gold potatoes for color variety.
  • Make ahead: assemble fully, refrigerate, and bake when needed.

Nutrition

Calories: 221kcalCarbohydrates: 36gProtein: 4gFat: 7gSaturated Fat: 1gPolyunsaturated Fat: 2gMonounsaturated Fat: 4gTrans Fat: 0.04gCholesterol: 1mgSodium: 299mgPotassium: 732mgFiber: 4gSugar: 6gVitamin A: 13IUVitamin C: 34mgCalcium: 43mgIron: 1mg
Keyword casserole, comfort food, gratin, heirloom recipe, homemade, onions, red potatoes, vintage recipe
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