1 tablespoon extra-virgin olive oil
2 slices bacon
1/2 cup (2 ounces) chopped white or yellow onion
2 large garlic cloves, minced or grated, about 1 tablespoon
1 1/2 pounds russet potatoes (2 to 3 medium), peeled and diced
4 cups no-salt chicken or vegetable low-sodium chicken broth
1/2 cup reduced-fat sour cream
1/2 cup (2 1/4 ounces) shredded extra-sharp cheddar cheese, divided
1/4 teaspoon freshly ground black pepper, or to taste
1/4 cup snipped fresh chives or finely chopped scallion greens, for serving
1/4 teaspoon ground white pepper
1/4 teaspoon kosher salt (optional)
Set a paper towel-lined plate or a rack near the stove. In a large saucepan over medium heat, add the oil and heat until shimmering. Add the bacon and cook, turning occasionally, until crisp, 4 to 5 minutes. Transfer to the prepared plate to drain, leaving the oil and bacon drippings in the pan.
Add the onion to the pan and cook, stirring, until starting to soften, about 3 minutes. Add the potatoes and broth and bring to a boil. Reduce the heat to medium-low to maintain a simmer. Cook until the potatoes are tender, about 15 minutes.
Using a slotted spoon, transfer about half the potatoes to a bowl and mash until almost smooth but still a little chunky. Return the potatoes to the pan along with the sour cream, 1/4 cup (about 1 ounce) of the cheese and the pepper.
Cook, stirring, until the cheese is melted and the soup is heated through, about 2 minutes. Taste and adjust seasoning, if needed.
Ladle the soup into bowls, garnish with the crumbled bacon, the remaining cheese and the chives or scallion greens, and serve.