4 pounds Yukon gold or russet potatoes, peeled and quartered
4 cloves garlic, peeled
1 teaspoon white vinegar
2-1/2 teaspoons kosher salt, divided
3 tablespoons unsalted butter, divided
6 ounces onions, peeled, ends cut flat
8 ounces low-fat cream cheese, cut into 1-inch pieces
¾ cup whole milk
1 large egg
¼ teaspoon freshly ground white pepper
Fill 4-quart sauce pan with potatoes and cover them by 1 inch of water. Add garlic, vinegar, and 1 teaspoon of salt. Bring to a boil and then lower heat to let them simmer for another 15-20 minutes, or until potatoes are tender.
Preheat oven to 350°F. Grease 3-quart ceramic baking dish with 1/2 tablespoon of butter.
Using the 4-mm slicing disc, push onions (side down) through feed tube of Cuisinart® Food Processor using medium pressure. Toss onions with 1 tablespoon of melted butter and 1/2 teaspoon of kosher salt. Set aside.
Switch to metal "s" blade and then add cream cheese, egg, and milk into work bowl. Blend until smooth and homogenous in texture (usually 1 minute). Remove ingredients and place in large bowl. Set aside.
Switch to medium shredding disc and then feed the drained potatoes in batches through the processor feed tube. Use light pressure for shredding. Transfer potatoes to large bowl, and add the cream cheese mixture, and remaining salt and pepper. Stir all ingredients together until blended.
Transfer potatoes to baking dish and layer the sliced onion on the top. After covering loosely with aluminum foil bake for 25 minutes. Remove foil and bake for another 30-35 minutes until mashed potatoes become puffy and onions are golden. Serve hot.