Heat olive oil in a skillet over medium heat. Add bacon; cook and stir until crisp. Add shallot and cook until softened, about one minute. Add mustard and vinegar; stir to combine. Season to taste with salt and freshly ground black pepper. Remove from heat.
Optional Step: to drain the watery white from each egg, crack egg over a large finely slotted spoon or fine mesh strainer set over a bowl; slide drained egg into a second small bowl or ramekin. Repeat with remaining eggs.
Meanwhile, in a saucepan, bring two inches of water to boil. Reduce heat to simmer. Stir water to create a vortex - this will help the whites stay together. Gently slide eggs into water, gently rotating them after 15 seconds and gently flipping after 2 minutes or so with a rubber spatula (be sure the yolk is facing up before lifting eggs out). Cook eggs until white is set, about 4 minutes. Lift each egg out with a slotted spoon and place on a paper towel to drain.
If your dressing has cooled, reheat it briefly. Pour dressing over frisee and toss toss to coat.
Divide salad between 4 serving plates and top each with a poached egg. Serve.
See notes in blog post about poaching eggs up to 5 days in advance.