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Cheesy potato casserole in a 9x13 dish with browned cheese, tomato slices and one portion served

Cheesy Potato Casserole

Mashed potatoes topped with dried herbs, mozzarella, parmesan, caramelized onion and tomato slices, baked in an 8-inch square dish at 425°F until browned.
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Prep Time 20 minutes
Cook Time 50 minutes
Total Time 1 hour 15 minutes
Servings: 6 servings
Course: Main Course, Side Dish
Cuisine: American
Ingredients Method Notes

Ingredients
  

  • 2 pounds russet or Yukon Gold potatoes 4 to 6 medium
  • 3 tablespoons unsalted butter divided
  • 1/4 cup half and half or nondairy milk
  • sea salt and pepper to taste
  • butter for the dish
  • flour for the dish
  • 2 cups (8 ounces) shredded mozzarella cheese
  • 1/2 cup grated parmesan cheese
  • 1 small onion sliced
  • 2 tomatoes sliced
  • 1 teaspoon dried oregano
  • 1 teaspoon dried basil
  • 2 teaspoons dried parsley

Method
 

  1. Heat the oven to 425°F. Butter an 8-inch square baking dish or a deep 9-inch pie plate, dust it with flour and tap out the excess.
  2. Peel the potatoes and cut any large ones in half. Boil them in a large pot of salted water for 20 to 25 minutes, until a fork slides in easily, then drain well.
  3. While the potatoes cook, melt 1 tablespoon butter in a skillet set over medium-high heat. Add the onion slices and cook, stirring often, for 10 to 12 minutes, until soft and golden brown; turn the heat down if the edges start to scorch. Set the onion aside.
  4. Mash the potatoes in a bowl with the remaining 2 tablespoons butter and the half and half, then taste and season with pepper and sea salt.
  5. Spread the mashed potatoes evenly in the dish and sprinkle the three dried herbs over them.
  6. Scatter on half of each cheese, cover with the caramelized onion, then lay the tomato slices over the onion. Finish with the rest of the mozzarella and parmesan.
  7. Bake for 20 to 25 minutes, until the top layer of cheese has melted and browned in spots and the center is hot (165°F on an instant-read thermometer).
  8. Let the casserole stand for 5 minutes before serving.

Notes

Nondairy milk can be used in place of the half and half.
Dish size: 2 pounds of potatoes makes a layer about 1 inch thick in an 8-inch square dish or deep 9-inch pie plate, the size used for versions of this dish baked as a pie. In a 9x13-inch dish the potato layer would be only about 1/2 inch thick, so double the recipe for that pan.
Make ahead: assemble the casserole, cover and refrigerate for up to 1 day. Bake uncovered at 425°F for 35 to 40 minutes, laying foil loosely over the top if the cheese browns before the center reaches 165°F.
Storage: refrigerate leftovers for 3 to 4 days and reheat until 165°F in the center.
Side options: salad, bread or tortilla chips.
Inspired by the Mozzarella and Potato Pie recipe in the Dallas Junior League cookbook.