Place 1 to 2 tablespoons olive oil in a large saute pan. Add the cut bacon and bring to a medium-high heat. Cook the bacon until it has become brown and crispy and a lot of fat has been rendered. This is a good thing!
Place the bacon and the fat into a bowl large enough to fit all of the ingredients. Add the vinegar and the blue cheese and stir to combine. Season with salt. Add the frisee and gently toss to combine. If a little more oil or vinegar is needed do so in small increments and taste as you go. The salad should be well seasoned and dressed but not soggy. Divide the salad onto 4 individual serving plates. Sprinkle with the chopped hazelnuts.