Here’s the recipe, at Suyin’s request. This is the magical mashed potato that tastes like sour cream and onion chips. It doesn’t contain onions, but does call for sour cream, buttermilk, and scallions.
Buttermilk Ranch Mashed Potatoes
5 lb Yukon Gold potatoes, peeled and cut into 1-inch chunks
14 tablespoons unsalted butter, melted and cooled
1 2/3 cup buttermilk, at room temperature
3 cloves garlic, minced fine
7 scallions, white and green parts sliced very thin
5 tablespoons minced fresh parsley leaves
1 cup sour cream
Ground black pepper
Place potatoes in large saucepan; add cold water to cover by 1 inch and 5 tablespoons of salt. Bring to boil over high heat, then reduce heat to medium and simmer until potatoes break apart when paring knife is inserted, about 18 minutes. Drain potatoes and return to saucepan set on still-hot burner.
Using potato ricer, rice potatoes into a large bowl. Gently mix melted butter and buttermilk in small bowl until combined. Add garlic, scallions, parsley, sour cream, salt and pepper to buttermilk mixture. Using rubber spatula, fold buttermilk mixture gently into mashed potatoes until just incorporated. Serve immediately or keep warm in a slow cooker for up to two hours.