1Heat oil in a large saucepan over medium heat. Add bacon and cook, turning occasionally, until crisp, 4 to 5 minutes. Transfer to a paper towel to drain, leaving the oil and bacon drippings in the pan.
2Add onion, carrots and celery to the pan and cook, sitrring, until starting to soften, 2 to 3 minutes.
3Add potatoes and broth. Bring to a boil. Reduce heat to maintain a simmer and cook until the potatoes are tender. 12 to 15 minutes.
4Using a slotted spoon, transfer about half the potatoes to a bowl and mash until almost smoth, but still a little chunky.
5Return potatoes to the pan, along with the sour cream and 1/4 cup of the cheese and pepper. Cook, stirring until the cheese is melted and the soup is heated through, 1 to 2 minutes. Serve garnished wtih crumbled bacon, the remaining cheese and chives.