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
# Directions:
01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Place peeled and chunked 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, stirring often, until golden and deeply caramelized, about 15-20 minutes. Add minced garlic during the last 2 minutes of cooking.
04 - Mash the drained potatoes with butter, warm milk, sour cream, 1 cup of the cheddar cheese, parmesan cheese, salt, and pepper until very smooth and creamy.
05 - Fold half of the caramelized onions into the mashed potato mixture. Taste and adjust seasoning with additional salt and pepper as needed.
06 - Spread the potato mixture evenly into the prepared baking dish. Top with the remaining caramelized onions and sprinkle the remaining 1/2 cup of cheddar cheese over the top.
07 - Bake uncovered for 20-25 minutes, or until the cheese is fully melted and bubbling.
08 - Let the casserole rest for 5 minutes. Garnish with fresh chives if desired, then serve warm.
# Expert Tips:
01 -
- Caramelized onions add a sweetness that makes people close their eyes on the first bite.
- It reheats beautifully so making extra is never a mistake.
- Sharp cheddar and parmesan together create a depth that a single cheese cannot pull off alone.
02 -
- Undercooked onions will taste sharp and raw so give them every minute they need to truly caramelize.
- Overworking the potatoes with a mixer can turn them gluey so a hand masher gives the best texture.
- The assembled casserole can be covered and refrigerated overnight then baked straight from the fridge with an extra ten minutes added.
03 -
- Warming the milk and softening the butter before adding them to hot potatoes prevents temperature shock and keeps the texture light.
- Dot the top with tiny cubes of extra butter before baking for an impossibly golden and rich crust.