Preparation

• In a 12-inch skillet, toss half of the breadcrumbs with 2Tbs. of the oil and 1/4tsp. salt. Cook over medium heat, stirring occasionally, until the crumbs brown and crisp, 3 to 5minutes. Transfer to a bowl and let cool.
• In a large bowl, using your hands, gently mix the beef and pork with 1tsp. salt and 1/2tsp. pepper. Gently mix in the Parmigiano, half of the parsley, the egg, capers, and remaining breadcrumbs. Set a small bowl of cold water nearby and, occasionally moistening your hands, gently roll 1-1/2-oz. portions of the meat into balls; you should get about 20.
• 擦拭煎锅并加热剩余的2汤匙。用中火加油，直到闪闪发光。煮一半的肉丸，不受干扰，直到底部变成褐色，约2分钟。另一侧翻转和褐色，越多1至2分钟。将煮熟的肉丸转移到衬有纸巾的盘子上，然后重复其余的肉丸。
• Pour off all of the fat, put the pan over medium-high heat, and add the chicken broth, vinegar, and sugar. Boil, stirring to incorporate any browned bits, until the mixture reduces by about half, 3 to 5 minutes.
• 将肉丸放回锅中，将热量降低到中等，煮锅，偶尔摇动锅，直到肉丸通过（160°F）煮熟，酱汁变稠到釉料，大约15分钟。（如果釉料在肉丸烹饪之前减少，请一次加入更多肉汤。
• Remove from the heat. Stir in the pine nuts and currants, and season to taste with salt and pepper. Serve sprinkled with the remaining parsley and toasted breadcrumbs.