Recipe reprinted from The Washington Post (February 18, 2015)
Melt the butter in a large saucepan over medium heat. Stir in the onion to coat; cook, stirring occasionally, for about 4 minutes or until the onion is somewhat translucent. Add the potatoes and hazelnuts; cook for 2 minutes, then pour in the water and cream. Increase the heat to medium-high; once the mixture comes to a boil, reduce the heat to medium and cook uncovered for about 25 minutes or until the potatoes are quite tender.
Stir in the sugar and the salt (to taste).
Working in batches, transfer the mixture to a blender. Remove the center knob of the blender lid, then cover the opening with a paper towel to allow steam to escape; puree until smooth and creamy. (You might wish to run the puree through the blender again, depending on which hazelnuts you used.)
Return the soup to the saucepan over medium-low heat; cook just until heated through. Taste, and adjust the seasoning as needed.
Divide among small bowls; garnish with some crushed pork rind and chopped hazelnuts, if using, and a drizzle of the oil. Serve hot.
NOTE: To skin hazelnuts, spread them on a rimmed baking sheet. Bake in a 350-degree oven for 10 to 15 minutes, until the skins look cracked. While the nuts are still quite hot, transfer to a dish towel; fold or close over the towel and rub vigorously to dislodge the skins. (This will make a mess.)
Adapted from "New German Cooking: Recipes for Classics Revisited," by Jeremy and Jessica Nolen (Chronicle, 2015).
Tested by Bonnie S. Benwick.