In a large bowl add pork, grated onion, garlic, baking powder, 1 teaspoon salt, nutmeg, allspice, and black pepper. Use your hand to mix and combine the mixture until consistent in appearance, 1 minute. Add in the breadcrumb mixture and mix with hand to combine until smooth, 1 minute. Add in ground beef and mix with hand until combined, 45 seconds. Roll meatball mixture into 2 tablespoon-sized balls, about 17 total.