Notes: If side bacon is not available, cut sliced bacon crosswise inot 1/4-inch pieces.
Tear frisée into bite-size pieces and place in a wide salad bowl.
Tear bread into 1/2-inch chunks and scatter over the greens.
Put bacon in a 10- to 12-inch nonstick frying pan over medium heat and stir often until browned and crisp, 10 to 12 minutes. With a slotted spoon, transfer to towels to drain.
Break eggs into drippings in pan, and when whites are firm on the bottom, slide a spatula under each egg and, if desired, carefully turn over. Cook until whites are no longer clear, about 1 minute total. With spatula, transfer eggs to a plate (place side by side); keep warm.
Quickly discard all but 2 tablespoons fat from pan. Turn heat to high, add vinegar and mustard, and whisk until mixture boils.
Pour hot dressing over frisee and bread, add bacon, and mix. Spoon into wide bowls and top each serving with a hot egg. Season to taste with salt and pepper.