Heat 2 to 3 inches of oil in a heavy-bottomed pot to 175 degrees C.
Carefully cut the potatoes into shoestrings (or matchsticks) using a mandolin fitted with the narrowest julienne blade (about 1/8-inch wide). Rinse the cut potatoes thoroughly in a bowl of cold water to remove the surface starch. Keep the potatoes in water until you're ready to fry.
For the aioli: Whisk together the mayonnaise, sour cream, truffle oil, garlic, lemon zest and salt and pepper to taste in a bowl. Refrigerate or set aside until ready to use.
Transfer the potatoes to a paper-towel-lined baking sheet and pat them dry, as dry as you can get them. I like to use a kitchen towel for this too; whatever gets them the driest.
Fry the shoestrings in batches until the potatoes are crisp and turn a nice golden brown, 2 to 3 minutes per batch. As each batch of fries comes out, transfer to a large mixing bowl and toss with some of the chopped herbs, a drizzle of the truffle oil and salt to taste. Transfer to a paper-towel-lined baking sheet. Serve with the truffle aioli.