Chips: Put an oven rack in the center of the oven. Preheat the oven to 350 degrees F.
Remove the thick stem from the kale and discard. Cut the leaves into 2 to 3-inch pieces. Put them in a bowl and drizzle with olive oil. Toss well. Arrange the kale in a single layer on parchment paper-lined baking sheets. Bake for 10 to 12 minutes until crispy and slightly dark on the edges. Season with salt and pepper, to taste.
Using a mandoline slicer or a sharp knife, slice the white potatoes and the sweet potatoes into 1/8-inch thick slices. Put them in a bowl and drizzle with olive oil. Toss well. Arrange in a single layer (without overlapping) on parchment-lined baking sheets and bake for 12 minutes. Turn the slices over and continue to bake, checking every 2 minutes until brown and crispy, about 6 to 8 minutes longer. Season the chips with salt and pepper, to taste.
Mayonnaise: In a small bowl, combine the mayonnaise, lemon juice and lemon zest. Season with salt and pepper, to taste.
Transfer all the chips to a large bowl and serve with the mayonnaise.
Some potato chips will cook faster than others. Remove the chips from the baking sheets as soon as they become brown and crispy. The recipe can be doubled or tripled.
Recipe courtesy of Giada De Laurentiis