Cheesy Onion Potato Casserole (Printable)
Creamy mashed potatoes with caramelized onions and melted cheddar, baked until golden and bubbly.
# What You Need:
→ Potatoes
01 - 2 lbs russet or Yukon Gold potatoes, peeled and cut into chunks
→ Dairy & Cheese
02 - 4 tbsp unsalted butter
03 - 1 cup whole milk, warmed
04 - 1 1/2 cups shredded sharp cheddar cheese, divided
05 - 1/2 cup grated Parmesan cheese
06 - 1/2 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 & Pantry
11 - 1 tsp salt, plus more to taste
12 - 1/2 tsp freshly ground black pepper
# How To Make It:
01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Place potatoes in a large pot and cover with cold, salted water. Bring to a boil, then reduce heat and simmer for 15-18 minutes, until fork-tender. Drain well.
03 - While the potatoes cook, heat olive oil in a large skillet over medium heat. Add sliced onions and sauté until golden and caramelized, about 15-20 minutes, stirring frequently. Add minced garlic during the last 2 minutes of cooking.
04 - Mash the drained potatoes with butter, warm milk, sour cream, 1 cup of cheddar cheese, Parmesan, salt, and pepper until very smooth and creamy.
05 - Gently fold half of the caramelized onions into the mashed potato mixture. Taste and adjust seasoning as needed.
06 - Spread the mashed potato mixture evenly into the prepared baking dish. Top with the remaining caramelized onions and the rest of the cheddar cheese.
07 - Bake uncovered for 20-25 minutes, or until the cheese is melted and bubbling.
08 - Let the casserole cool for 5 minutes. Garnish with fresh chives if desired, then serve.
# Expert Suggestions:
01 -
- The caramelized onions disappear into the potatoes like a secret that only reveals itself when someone asks what makes it taste so good.
- You can assemble the entire thing a day ahead, which means you get to actually enjoy your own gathering instead of being trapped in the kitchen.
02 -
- Under salted mashed potatoes are nearly impossible to fix once they are baked, so taste the mashed mixture before it goes into the dish and be generous.
- Warming the milk and melting the butter before adding them to the potatoes prevents that gummy, paste like texture that ruins otherwise perfect spuds.
03 -
- Run your potato masher or fork through the drained potatoes while they are still hot and steam is rising, because that steam is moisture you want escaping before the dairy goes in.
- A handful of extra cheese scattered over the top in the last five minutes of baking creates those irresistible browned cheese bits that everyone fights over.