Place the sliced potatoes in cold water then stir. Drain and refill with water, continuing until the water runs clear. Return to a bowl covered with water and add the vinegar.
In a large heavy bottom pot over medium heat, add enough oil to reach at least 2” up the side of the pot. Heat the oil to 300ºF (150ºC). Once the oil is heated, remove the potatoes from the water and dry with paper towels.
Fry the potatoes in batches, stirring with a metal spoon as they cool. Fry until they are crisp and golden brown, about 5 minutes. Remove to a paper-towel-lined plate to drain and season with salt. Repeat with the remaining sliced potatoes.
For the blue cheese béchamel:
In a small saucepan over medium heat, add butter and allow to melt. Add shallot and sauté until tender, about 4 minutes.
Add the flour and whisk to combine. Let the roux cook for a minute until a pale golden brown. Add the milk, whisking to incorporate. Bring the mixture to a boil then lower the heat to medium-low.
Cook, whisking occasionally, until the sauce coats the back of a spoon, about 10 minutes. Add ¼ cup of the blue cheese, whisking to combine. Remove the béchamel sauce from heat and set aside.
For serving:
Arrange the chips in a large serving bowl and pour the béchamel over the top. Top with the crumbled blue cheese, bacon, tomato and chives.