Sour Cream and Onion Mashed Potato Casserole Recipe (Make-Ahead)

Mashed potatoes have never been a favorite of mine. In fact, potatoes are probably my least favorite carb (with the exception of potato chips, which are my FAVORITE carb). I just find most potatoes kind of boring. Phew, glad I got that off my chest! 

Now that that’s out of the way, there are many potato dishes I really enjoy. I’ll house a plate of fries (hold the ketchup), and I’ll happily munch on some crispy roasted potatoes with herbs and garlic.

But mashed potatoes, with their lack of exciting flavors and textures, were just never my jam. That is, until one fateful Christmas day, when my mom replaced standard mashed potatoes with this delightfully cheesy, oniony, tangy, crispy-bits-on-top mashed potato casserole. 

Mashed Potatoes, but Better

This amped-up version of classic mashed potatoes has bigger, bolder flavors and a crispy golden brown top that upgrades mashed potatoes in a way you never knew you needed. 

The additional prep work—grating cheese and slicing scallions—is minimal and more than compensated for by the fact that this casserole can be fully prepared days in advance and popped into the oven right before dinner.

I highly recommend freshly shredding your cheese rather than buying pre-shredded. Pre-shredded cheese will not melt correctly due to the anti-caking agents added. 

Serving Suggestions

This dish quickly became a staple for every major holiday dinner in our family. I would literally beg my mom to make it. While it’s a super versatile side dish, it pairs particularly well with turkey and ham, as the savory onion and tangy sour cream nicely contrast the sweetness of the ham and the mildness of the turkey.