In a 5- to 6-quart pan, stir bacon over medium-high heat until lightly browned and crisp, about 10 minutes. Lift from pan with a slotted spoon and drain on paper towels.
Add onion to pan drippings and stir often until limp, about 3 minutes.
Meanwhile, cut potatoes into 1/2-inch cubes.
Add potatoes and broth to pan. Cover and bring to a boil over high heat. Reduce heat to low and simmer until potatoes are tender when pierced, about 10 minutes, stirring occasionally.
Blend flour and milk until smooth. Add to soup and stir over high heat until boiling, about 3 minutes.
Stir in parsley and ladle soup into bowls. Sprinkle with bacon and season to taste with salt and pepper.