Meanwhile, make the dressing. Cook the bacon in a skillet over medium heat until crispy. Take out the bacon and set it aside, leave the rendered fat in the pan. Add the onion to the pan and saute until translucent but not browned, about 3-4 mins (Image 1). Add beef broth and bring to a simmer. Turn down the heat and add vinegar, mustard, oil, sugar, salt, and pepper (Image 2).
6-8 slices bacon, ½ cup finely chopped onion, ¾ cup beef broth, 6 tablespoons white vinegar, 1 teaspoon mustard, 2 tablespoons vegetable oil, 1 teaspoon sugar, ½ teaspoon salt, ¼ teaspoon black pepper