2 lb. baby Yukon Gold potatoes
1 cup kosher salt, plus more
¾ cup sour cream
¼ cup mayonnaise
1 Tbsp. onion powder
2 tsp. Dijon mustard
1 tsp. freshly ground black pepper
1 garlic clove, finely grated
1 bunch chives, thinly sliced, divided
¼ small red onion, very thinly sliced through root end
½ cup sour cream and onion potato chips
Place potatoes in a large pot and pour in 3 qt. water to cover. Add 1 cup salt and bring water to a boil over medium-high heat. (Yes, this is a lot of salt, but it’s the right amount to ensure potatoes are seasoned through and through.) Reduce heat and simmer, adjusting heat as needed, until potatoes until fork-tender, 15–20 minutes. Scoop out ½ cup potato cooking liquid and set aside. Drain potatoes in a colander and let sit until cool enough to handle, about 10 minutes.
Meanwhile, combine sour cream, mayonnaise, onion powder, mustard, and pepper in a large bowl and mix well to combine. Add garlic and half of chives and mix just to incorporate.
Place red onion in a fine-mesh sieve and rinse for several seconds to take away some of its raw bite. Pat dry with paper towels. Mix half of onion into dressing; set aside remaining onion for serving.
Working one at a time, set potatoes on a flat surface and crush slightly with the palm of your hand. Add to bowl with dressing along with ¼ cup potato cooking liquid. Do this while the potatoes are still warm so that they can absorb all of the seasoning. Don’t worry if the dressing looks a little loose and watery at the beginning—it will all get absorbed and become creamier as it sits. Taste and season with more salt or, if your dressing looks too thick, a splash of potato cooking liquid.
Top potatoes with remaining chives and reserved onion and crumble potato chips over.