Veal Meatballs with Mustard Greens

Name: Veal Meatballs with Mustard Greens
Ingredients: 1/4 cup extra-virgin olive oil; 1 cup minced onion; 2 garlic cloves, minced; 1/2 teaspoon ground fennel seeds; 1/4 teaspoon mustard powder; 1/4 teaspoon crushed red pepper; 1/4 teaspoon ground coriander; 1/4 teaspoon chipotle or other smoked chile powder; 1 pound ground veal; 1/2 cup fresh bread crumbs (2 ounces); 1/4 cup heavy cream; 1 large egg, lightly beaten; 1/2 teaspoon kosher salt; 1/2 pound mustard greens, thick stems discarded and leaves chopped; 1/3 cup chicken stock or low-sodium broth