How to Make It
Make the broth: In a large saucepan, spread pork and ham in a single layer, and cook over moderately low heat, undisturbed, until browned on the bottom, about 7 minutes. Stir meat and continue cooking, stirring occasionally, until well browned, about 5 minutes. Add 1/2 cup water; scrape up browned bits from bottom of pan. Add chopped onion, chopped carrot, celery, garlic, thyme sprigs, bay leaves, peppercorns, coriander, and remaining 2 quarts water. Bring to a boil. Cover and simmer over moderately low heat for 2 hours. Strain broth into a heatproof bowl; discard solids. Return broth to pan; bring to a boil, and cook until reduced to 1 quart. Skim any foam from surface. Season lightly with salt.
Meanwhile, prepare the vegetables: In a medium bowl, combine mustard greens, sugar, and 1 teaspoon salt. Massage greens until wilted. Let stand 1 hour.
Preheat oven to 400°F. Toss carrot pieces with 2 tablespoons oil and salt on a large parchment-lined baking sheet. Spread in an even layer, and roast until caramelized and tender, about 30 minutes.
Make the meatballs: In a medium skillet, heat 3 1/2 tablespoons oil until shimmering. Add diced onion, garlic cloves, chopped thyme, and 1/2 teaspoon salt. Cook over moderate heat, stirring occasionally, until softened and browned, about 10 minutes. Cool completely.
In a large bowl, stir together breadcrumbs and milk; let stand until absorbed, about 5 minutes. Add pork, egg, onion mixture, and remaining salt; stir well. Form mixture into 1 1/2-inch meatballs and arrange on a parchment-lined baking sheet. Refrigerate until chilled, about 30 minutes.
Roast meatballs at 400°F until browned and cooked through, 20 to 25 minutes.
Bring broth to a simmer over moderate heat. Add cream, meatballs, carrots, and mustard greens, and simmer until hot, about 5 minutes. Transfer to 4 bowls, and garnish with chopped parsley and dill.