In a pot, bring salted water to a simmer and add 1 tbsp (15 ml) of the vinegar. Break the eggs, one at a time, into a small ramekin. Slide them into the water one at a time. Poach for 2 to 3 minutes, or until the desired doneness. The yolks should be runny and the whites cooked through but still soft. Remove with a slotted spoon and drain on paper towels. Set aside.
In a small bowl, cover the red onion with the remaining vinegar and set aside while you prepare the rest of the ingredients.
In a large non-stick skillet over medium-high heat, toast the bread cubes in the butter, tossing them until golden on all sides. Transfer to a large bowl.
In the same skillet, cook the bacon until crispy. Drain and add to the bread, tossing to combine, along with the lettuce and endive.
In a bowl, whisk together all the ingredients. Drain the onion, adding the vinegar to the dressing and the onion to the salad.
Arrange the salad on plates. Top with the poached eggs and season with salt and pepper. Drizzle with the dressing.