The key to perfect, fluffy spuds is not overworking them with an electric mixer; a ricer (or food mill, if you have one) or potato masher is the best tool for the job.
Place potatoes in a large saucepan; cover with water. Bring to a boil; reduce heat, and simmer 15 minutes or until tender. Drain. Press potatoes through a ricer back into pan, or mash with a potato masher to desired consistency.
Add buttermilk, milk, melted butter, kosher salt, and white pepper to potato mixture; stir well. Top with chopped fresh chives.