Putting mashed potatoes on pizza is a slightly assholeish thing to do—you’re topping carbs with ... more carbs—but when it works, it’s comforting and slightly naughty stoner food turned up to eleven. It’s also something chain pizzerias would do. Like mashed potato– loaded potato skin pizza (the first mashed potato pizza I made was a loaded potato skin pizza with speck, a beautiful Vermont Cheddar, and freshly chopped chives, and it was amazing).
If you do put mashed potatoes on a pizza, they should be fucking awesome.