Cheesy Onion Mashed Potatoes (Printable)
Creamy mashed potatoes with caramelized onions and melted cheddar, baked until 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, warmed
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 fresh chives, chopped (optional, for garnish)
→ Spices & Seasonings
11 - 1 tsp salt, plus more to taste
12 - ½ tsp freshly ground black pepper
# Directions:
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 15–18 minutes. Drain thoroughly.
03 - While the potatoes cook, heat olive oil in a large skillet over medium heat. Add the sliced onions and sauté, stirring occasionally, until deep golden brown and caramelized, about 15–20 minutes. Add the minced garlic and cook for 1 additional minute.
04 - Mash the drained potatoes together with the butter, warm milk, sour cream, salt, and black 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 the reserved caramelized onions.
07 - Bake for 25 minutes, or until the cheese is melted, bubbly, and lightly golden in spots.
08 - Remove from the oven and garnish with fresh chives if desired. Serve hot.
# Expert Tips:
01 -
- The caramelized onions melt into the potatoes so completely that even onion skeptics come back for seconds.
- It reheats beautifully, making it the rare leftover that tastes just as good three days later.
02 -
- Gummy mashed potatoes are almost always caused by overmixing or adding cold liquid, so warm the milk and stop mashing the moment everything comes together.
- Undercaramelized onions taste like slightly sweet raw strips, so give them the full time and watch for that deep amber color before moving on.
03 -
- Dry your boiled potatoes in the hot pot for one minute off the heat before mashing, because excess water is the enemy of rich, creamy texture.
- Use a combination of cheeses you genuinely love eating on their own, because the casserole will only taste as good as what you put into it.