I used this when the need for a quick side dish coincided with leftover mashed potatoes, but it's nice enough to serve to company.
3 cups leftover mashed potatoes
1 cup cheese - I used a mixture of grated Parmesan, grated Gruyère, and shredded old/sharp cheddar
3 TB minced chives
Mix all of the above. Season to taste with salt and pepper, taking into account that if the mashed potatoes are leftovers they were already seasoned.
Spray a non-stick muffin tin. Use a scoop to divide the mixture evenly into the 12 cups. [Can be made ahead to this point.] In an oven pre-heated to 375 F, bake for 30-35 minutes or until the potatoes are nicely browned. Remove and sprinkle with a bit of grated cheddar. Return to the oven (or broiler) just long enough to melt the cheese and serve as soon as possible. [One website did suggest removing them from the muffin tin, storing them refrigerated, then placing them on a baking sheet to reheat – 400 F for 10-15 minutes.]
I can see adopting this as a useful way to use leftover mashed. One observation - my non-stick muffins pans are not so “non-stick” anymore, so removing the little potato “muffins” was a bit tricky in a few cases. Next time I may add a little folded parchment sling to the muffin cups so they will lift out more easily – or… I could get new tins since those I have are from the last century!