1 medium onion, cut into 8 wedges
2 pounds Yukon Gold potatoes, peeled and cut into quarters, or into sixths if the potatoes are large
2 tablespoons unsalted butter
2 large egg yolks, plus 1 whole egg
1/2 teaspoon salt
1/2 teaspoon freshly ground black pepper
2 tablespoons heavy whipping cream
2/3 cup plain fine dried bread crumbs (may substitute finely grated Parmigiano-Reggiano cheese for half of the bread crumbs)
1/4 cup finely chopped flat-leaf parsley
1. Line a work surface with a few layers of paper towels. Fill a large pot with several inches of water, add the onion wedges, and bring to a boil over high heat. Reduce the heat to medium and cook until the onion is very soft, about 40 minutes, keeping the water at a low boil. Use a slotted spoon to transfer the onion to a colander and allow to drain for several minutes, then transfer to the paper towels. Use more paper towels to press on the onion, extracting as much of the moisture as possible. Transfer to a blender and puree until smooth.
2. Preheat the oven to 350 degrees. Grease a baking sheet with nonstick cooking oil spray.
3. Add the potatoes to the water in the pot; add water if needed to cover the potatoes by 1 inch. Increase the heat to medium-high and bring to a boil, then reduce the heat to medium and cook uncovered for 12 to 15 minutes or until the potatoes can be easily pierced with the tip of a knife. Drain in a colander. Return the empty pot to the stove over medium heat.
4. Return the potatoes to the pot and cook, tossing, for 1 to 2 minutes or until their moisture has evaporated. Use a potato ricer to shred the potatoes into a large mixing bowl, or place the potato pieces in the mixing bowl and mash with a potato masher.
5. Add the pureed onion to the potatoes and combine, then quickly beat in the butter and egg yolks. Add the salt and pepper. Beat in 1 to 2 tablespoons of cream, keeping the mixture thick enough to hold its shape; if it is too thin, return the mixture to the pot over medium heat and cook, stirring constantly, to dry it out a little.
6. Use a fork to beat the remaining whole egg in a small bowl. Spread the bread crumbs on a small plate. Use your hands to form the potato mixture into 21 golf-ball-size balls (about 11/2 ounces each). Brush the balls with the beaten egg and sprinkle with a little parsley, then dip them in the crumbs, rolling to coat evenly. Transfer to the prepared baking sheet.
7. Bake for 20 minutes, until heated through. The potato balls will brown slightly. Serve hot.
Note: The potato mixture can be covered and refrigerated a day in advance; or the balls can be formed and rolled in the crumbs and then refrigerated, loosely covered, a day in advance. Bring to room temperature before baking.
Per serving (based on 7): 200 calories, 4 grams protein, 32 grams carbohydrates, 3 grams sugar, 7 grams fat, 80 milligrams cholesterol, 240 milligrams sodium, 3 grams dietary fiber