Begin by soaking the cashews for the chipotle aioli. Place the cashews into a bowl or a glass jar. Pour boiling water over the cashews, just enough to cover them. Let the cashews sit for 45 minutes to an hour.
To make the roasted fingerling potatoes, preheat oven to 400ºF. Set an oven rack in the center position. Line a large sheet pan with parchment paper and set aside.
Rinse the fingerling potatoes. Slice the potatoes in half. If you have larger fingerling potatoes, slice them into quarters. Toss the potatoes with the olive oil and a pinch of salt.
Spread the potatoes over the prepared baking sheet. Arrange the potatoes so that they are cut side down. Bake the potatoes for 30 minutes.
Take the potatoes out of the oven and increase the oven temperature to 425ºF. Lift the potatoes and check their color. If they are a deep golden brown, flip them over. Many ovens don't roast the potatoes evenly, so you may end up flipping about half of the potatoes only. Return the potatoes to the oven and roast for another 8 to 10 minutes.
While the potatoes are baking, prepare the chipotle aioli. Drain the cashews. Using a high-speed blender or an immersion blender, blend the cashews, filtered water, lemon juice, chipotle peppers, garlic, chives, salt and chili seasoning until smooth. Drizzle in the olive oil and blend until incorporated. Pour the chipotle aioli into a bowl and let it sit until the potatoes are finished baking.
Sprinkle the potatoes with a bit of black pepper and chopped chives, if you like. Serve the potatoes with the aioli.
You can also soak the cashews overnight with filtered water. Soaking cashews in room temperature water preserves the enzymes in the cashews.If you want the aioli to be less spicy, use 2 chipotle peppers.