Vegetable or canola oil, for frying (about 6 cups in a deep skillet or 2 qt. in a tabletop fryer)
1 ¼ cups dry breadcrumbs
¼ cup whole milk
1 ¼ lb. ground pork
About 3 tbsp. grated onion with juices
Salt and freshly ground black pepper
2 large eggs plus 1 large egg yolk
¼ cup fresh flat-leaf parsley tops, finely chopped
1 tbsp. fresh lemon zest or about 1 tsp. dried lemon zest
1 tsp. (about 1/3 palmful) dried thyme
½ tsp. ground white pepper
About 1/8 tsp. freshly grated nutmeg
1 cup flour
Flaky sea salt, cornichons, lemon wedges, and 1/2 cup Dijon mustard (smooth or grainy), for serving
In a large deep skillet or a tabletop fryer, preheat the oil to 360°. Preheat the oven to 250°. Set a wire rack inside a baking sheet.
In a medium bowl, mix 1/4 cup breadcrumbs and the milk. Let stand until the crumbs soften, 3 to 5 minutes. Add the pork and onion with juices. Season with salt and pepper. Mix in the egg yolk, half the parsley, the lemon zest, thyme, white pepper, and nutmeg. Roll the mixture into balls about the size of a large walnut.
In a shallow bowl, place the flour. In a second shallow bowl, beat the 2 eggs. In a third shallow bowl, add the remaining 1 cup breadcrumbs.
Working in batches, roll the meatballs in the flour; coat with the eggs and then the breadcrumbs, pressing gently so the crumbs adhere. Place on a second baking sheet. Working in batches of 7 to 8, fry the meatballs, turning once, until golden and cooked through, 3 to 4 minutes per batch. Transfer to the wire rack in the baking sheet. Season with flaky salt. Place the baking sheet in the oven to keep the meatballs warm between batches.
Arrange the meatballs on a platter. Garnish with the remaining parsley. Serve with cornichons, lemon wedges, and mustard.