• Bring a large pot of water to a boil and add 1 tablespoon salt. Add the green beans and cook until just tender, 3-4 minutes. Drain and immerse in ice bath. Drain and spread out on paper towels to thoroughly dry.
• Meanwhile, in a medium skillet, cook the bacon over medium heat until crisp, 6 to 8 minutes; transfer to a paper towel-lined plate. Let cool, then break into pieces.
• Discard all but 1 tablespoon of the bacon drippings from the skillet and return to medium heat. Add the shallots and cook, stirring, for 1 minute and remove.

Dressing:

• Combine vinegar, mustard, oil, ¾ teaspoon salt, and ¼ teaspoon pepper. Add to the green beans, along with the bacon, and toss to combine.