Heat a non-stick skillet over medium heat. Add the bacon and cook, stirring occasionally, until crisp, about 4-5 minutes. Cook in batches if needed. Transfer the bacon to a paper towel-lined plate with a slotted spoon and set aside. Reserve then strain 1 tablespoon of the bacon grease.

Melt the butter with the reserved bacon grease in a large Dutch oven over medium heat. Stir in the onion with 1 teaspoon of the salt. Cook for 5-7 minutes, stirring occasionally until softened. Add the potatoes and garlic and cook for another minute. Add the chicken stock and evaporated milk, then bring to a boil and reduce to a rolling simmer. Cook until the potatoes are fork-tender and the soup has reduced, for about 10 minutes.

Spoon a few tablespoons of the broth into a small bowl and whisk in the cornstarch a bit at a time to create a slurry. Once smooth, add the slurry back to the soup to simmer and thicken. Season with the rest of the salt to taste.

Ladle half of the soup with potatoes into a blender and process for about 30 seconds until smooth. Return the blended portion of soup to the pot and cook on medium for about 5 minutes, stirring occasionally until the soup thickens. To serve, ladle the soup into bowls, and top with crumbles of the cooked bacon, shredded cheddar cheese, a dollop of sour cream, and chives.