In a small bowl, combine breadcrumbs and milk. Let soak for 5 minutes until breadcrumbs absorb all liquid.

In a large mixing bowl, combine ground chicken, soaked breadcrumbs, minced onion, garlic, egg, parsley, salt, pepper, nutmeg, and lemon zest. Mix gently until evenly combined.

With damp hands, shape mixture into 12-14 meatballs about 2 inches in diameter. Place on a plate as you form them.

In a large deep skillet or Dutch oven, bring chicken broth and white wine to a gentle simmer over medium heat.

Carefully lower meatballs into simmering liquid. Poach gently for 15-18 minutes, turning occasionally, until cooked through. Remove with slotted spoon and set aside.

Strain cooking liquid through fine-mesh sieve. Reserve 2.5 cups of this broth for the sauce.

In the same pan, melt butter over medium heat. Add flour and whisk constantly for 2-3 minutes to create a smooth roux.

Gradually whisk in reserved cooking liquid. Continue whisking until sauce thickens, about 5-7 minutes.

Reduce heat to low. Stir in heavy cream, capers, lemon juice, and Dijon mustard. Season with salt and white pepper to taste.

Return meatballs to sauce and warm through for 3-5 minutes. Garnish with fresh parsley and serve immediately.