Saute the bacon until crisp.
Skim out and add to the lettuce.
Saute the onion lightly in the bacon fat.
Stir in the flour and blend.
Stir the vinegar into this mixture.
If the vinegar is rather sharp dilute it with a little water.
Stir until smooth, season to taste, and pour over the lettuce.
Toss well, until the lettuce is a little wilted, and serve at once, while still warm.
This is the so-called "wilted lettuce" liked by so many people.