Luchow's German Potato Salad

1 pound (3 medium) potatoes
6 slices bacon, diced
1 medium−size onion, diced
1/2 cup vinegar
1/2 cup stock or bouillon
1 tsp. salt
1/4 tsp. pepper
1 tsp. sugar
1 egg yolk, beaten
Serves 2−4.
Scrub potatoes; rinse. Boil in jackets; let cool.
Peel and cut in 1/4−inch slices.
Cook bacon in hot pan until crisp.
Add onion; stir and cook until transparent.
Add vinegar, stock or bouillon, and seasonings.
Stir; let come to a boil.
Stir in egg; remove from heat and pour over potatoes.