Potatoes: one of the most filling budget-friendly foods out there! This recipe for Mashed Potato Casserole will fill up everybody’s holiday plate for pennies. Even better, I can make this ahead of time and pop it in the oven day-of to finish. It’s the perfect side dish for when I want to maximize time spent with loved ones instead of standing over a hot stove all day. Topped with crumbled bacon, gooey cheese, and a handful of green onions, this easy casserole has become a new family favorite.
What is Mashed Potato Casserole?
Mashed potato casserole is the best way to prep mashed potatoes ahead of time. The potatoes are mashed and mixed with onions, garlic, sour cream, milk, and seasonings, then topped with a layer of cheese, green onions, and crispy bacon. It’s like our loaded potato soup but in casserole form! My family loves the creamy potatoes with the salty bacon and melted cheese—it’s hearty, comforting, and a must-make this holiday season.
Ingredients
Here’s what you’ll need to make this cheesy mashed potato casserole:
- Bacon: Cook the bacon in the oven until crispy before crumbling and topping your casserole! Vegetarian? Use your favorite veggie bacon substitute, or leave it out completely.
- Russet Potatoes: I usually reach for Russet or Yukon gold potatoes when making mashed potatoes. Both are high-starch potatoes, which means they’re great for mashing and making the fluffiest, creamiest potatoes. I opted for Russet in this recipe because they’re cheaper, but you can use whatever kind you prefer.
- Water: You need enough water to cover the potatoes for boiling.
- Salted Butter: Use this to grease your baking dish and to make your potatoes extra buttery and rich!
- Yellow Onion & Garlic: These aromatics add a delicious depth of flavor to your casserole.
- Whole Milk: Helps make your potatoes creamy and smooth. It’s also lighter and more cost-effective than heavy cream.
- Sour Cream: Adds a subtle tangy flavor and even more creaminess.
- Shredded Parmesan & Shredded Cheddar: If possible, shred your own cheese rather than buying pre-shredded. Pre-shredded cheeses often include anti-caking agents that can affect the melt and texture of the cheese.
- Seasonings: I use salt, black pepper, smoked paprika, and chili flakes (optional), but feel free to adjust the seasonings to your liking. You’ll also need a little salt to season the water the potatoes boil in.
- Green Onions: Dice 2 green onions and sprinkle them on top after baking. They add to the ‘loaded’ flavor in this casserole recipe and go great with the bacon and cheese!
How to Fix Gummy Potatoes
Mashed potatoes can get thick and gummy if they’re overworked or if the excess starch isn’t properly removed. That’s why I recommend rinsing the diced potatoes twice (before and after boiling) to wash away extra starch. I’ve also noted in the recipe not to overmix the potatoes when mashing. But if, despite your best efforts, your potatoes still turn out gummy, don’t worry! Add 1 Tbsp of additional butter at a time, stirring to combine, until you like the texture better. 1 Tbsp of butter per pound of potatoes usually does the trick. You can then assemble your mashed potatoes casserole as directed and bake!
Make Ahead Instructions
I mentioned earlier how this casserole can be made ahead—it’s such a time saver! Assemble the casserole as directed, cover it with plastic wrap, and store it in the fridge for up to two days before baking. When you’re ready to cook, let it come to room temperature for about 30 minutes, remove the plastic wrap, and then bake as directed. So easy!
Serving Suggestions
Like our potato casserole (which is made with diced potatoes, not mashed), this easy casserole is a great side for any occasion. It’s much easier to keep warm than traditional mashed potatoes, and the cheesy topping stops it from drying out. It’s the perfect Christmas or Thanksgiving side dish (don’t forget the gravy!), but it also goes well with almost any main! A saucy dish, like our chicken meatballs in cream sauce, would be a great pairing with steamed veggies and crusty bread.
How to Store
Any leftovers can be kept in the refrigerator for 3-4 days. Either cover the casserole dish or portion out individual servings and store them in airtight containers. This loaded mashed potato casserole is best reheated in the oven (cover with foil if the bacon and cheese are getting too crispy) but can also be reheated in the microwave. While you can freeze this casserole for 2-3 months, the sour cream in the potatoes may separate a bit when thawed, so keep that in mind.
Mashed Potato Casserole Recipe
Equipment
- 9×13 Baking Dish
Ingredients
- 6 strips bacon $1.74
- 3 lbs russet potatoes* $1.95
- water** $0.00
- ½ tsp salt $0.01
- 5 Tbsp salted butter (plus a little extra to butter your casserole dish) $1.25
- ½ yellow onion, diced small $0.47
- 3 cloves garlic, minced $0.09
- ½ cup whole milk $0.14
- ¼ cup sour cream $0.31
- ½ tsp freshly cracked black pepper $0.05
- ½ tsp smoked paprika $0.08
- salt, to taste (I added about 1 tsp) $0.01
- ¼ tsp chili flakes (optional) $0.06
- ¼ cup shredded parmesan $1.07
- ½ cup shredded cheddar $0.56
- 2 green onions (about 2 Tbsp), diced $0.15
Instructions
- Preheat your oven to 400ºF. Cook bacon in the oven until crispy.
- Once cooked and crispy, drain your bacon on paper towels. Set aside for now.
- Peel potatoes and dice them into 1–2-inch cubes, rinse well.
- Put potatoes in large pot, covered by 2 inches of water. Add ½ tsp salt.
- Boil until fork-tender (on the softer side), about 15-20 minutes.
- Drain potatoes and rinse with warm water. Set aside. Rinse out potato pot briefly and give it a quick wipe.
- Melt salted butter in the potato pot and add onion. Cook until soft and glossy.
- Add minced garlic and cook for 2 minutes until fragrant.
- Add cooked potatoes back to pot with onions and garlic. Mash with potato masher until they are the consistency you prefer, being careful not to overmix to avoid a gummy texture.
- Add whole milk, sour cream, pepper, smoked paprika, salt (to taste), and chili flakes (optional) and combine.
- Butter a 9×13” casserole dish. Transfer potatoes to the buttered casserole dish and smooth out with a spatula.
- Top with shredded parmesan, shredded cheddar, and crumbled bacon.
- Bake in oven at 400ºF for 20 minutes covered with foil, then uncover for 10 minutes.
- Garnish with green onions and serve.
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Notes
Nutrition
how to make Mashed Potato Casserole – step by step photos
Preheat your oven to 400ºF. Cook 6 strips bacon in the oven until crispy.
Once cooked and crispy, drain your bacon on paper towels. Set aside for now.
Peel 3 lbs russet potatoes and dice them into 1–2-inch cubes, rinse well.
Put potatoes in large pot, covered by 2 inches of water. Add ½ tsp salt.
Boil until fork-tender (on the softer side), about 15-20 minutes.
Drain potatoes and rinse with warm water. Set aside. Rinse out potato pot briefly and give it a quick wipe.
Melt 5 Tbsp salted butter in the potato pot and add ½ a diced yellow onion. Cook until soft and glossy.
Add 3 cloves minced garlic and cook for 2 minutes until fragrant.
Add cooked potatoes back to pot with onions and garlic. Mash with potato masher until they are the consistency you prefer, being careful not to overmix to avoid a gummy texture.
Add ½ cup whole milk, ¼ cup sour cream, ½ tsp pepper, ½ tsp smoked paprika, salt (to taste), and ¼ tsp chili flakes (optional) and combine.
Butter a 9×13” casserole dish. Transfer potatoes to the buttered casserole dish and smooth out with a spatula.
Top with ¼ cup shredded Parmesan, ½ cup shredded cheddar, and crumbled bacon.
Bake in oven at 400ºF for 20 minutes covered with foil, then uncover for 10 minutes.
Garnish with 2 diced green onions and serve. You’ll never look back once you try this make ahead mashed potato casserole—it’s the ultimate comfort food!
More Mashed Potato Recipes
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A healthier take on this comfort food staple. 
