Cheesy Onion Mashed Potato Casserole (Printer-Friendly)
Creamy mashed potatoes with caramelized onions and melted cheese, baked golden and bubbly.
# What You'll Need:
→ Potatoes
01 - 2 lbs russet or Yukon Gold potatoes, peeled and cubed
→ Dairy
02 - 1 cup whole milk
03 - 4 tbsp unsalted butter, plus extra for greasing
04 - 1 ½ cups shredded sharp cheddar cheese
05 - ½ cup shredded mozzarella cheese
06 - ½ cup sour cream
→ Vegetables
07 - 2 large yellow onions, thinly sliced
08 - 2 tbsp olive oil
09 - 2 cloves garlic, minced
10 - 2 tbsp chopped fresh chives (optional, for garnish)
→ Spices & Seasonings
11 - 1 tsp salt, plus more to taste
12 - ½ tsp freshly ground black pepper
# How to Make It:
01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish with butter.
02 - Place the peeled and cubed potatoes in a large pot of salted water. Bring to a boil, then reduce heat and simmer until fork-tender, about 15 to 18 minutes. Drain thoroughly.
03 - While the potatoes cook, heat olive oil in a large skillet over medium heat. Add the thinly sliced onions and sauté, stirring occasionally, until golden brown and deeply caramelized, about 15 to 20 minutes. Add the minced garlic and cook for 1 additional minute.
04 - Mash the drained potatoes with butter, warm milk, sour cream, salt, and pepper until smooth and creamy.
05 - Stir half of the cheddar and mozzarella cheeses into the mashed potatoes, then gently fold in the caramelized onions. Reserve a few tablespoons of onions for the topping if desired.
06 - Spread the potato mixture evenly into the prepared baking dish. Top with the remaining cheddar and mozzarella cheeses and any reserved caramelized onions.
07 - Bake for 25 minutes, or until the cheese is melted, bubbly, and lightly golden in spots.
08 - Garnish with fresh chives if desired. Serve hot.
# Expert Advice:
01 -
- The caramelized onions melt into the potatoes so completely that even picky eaters barely notice them, but they add a sweetness that makes people wonder what your secret is.
- It reheats beautifully the next day, which means lunch is sorted and you get to enjoy it all over again.
02 -
- Do not rush the onion caramelization because cranking the heat to speed things up gives you burnt edges and raw centers instead of that deep sweet jamminess.
- Drain the potatoes really well and even return them to the hot pot for a minute to steam off excess water because soggy potatoes make a wet casserole that never sets.
03 -
- Taste the mashed potatoes for salt before you spread them into the dish because once that cheese goes on top, fixing the seasoning underneath becomes impossible.
- Let the casserole rest for those five minutes after baking because the cheese needs to settle and the whole thing holds together better when you scoop it.