Stir the tomatoes, broth, bell pepper, onion, carrot, basil or oregano, thyme, salt, and nutmeg in the cooker.
Mix the ground beef, sausage meat, egg, breadcrumbs, and milk in a large bowl until uniform. With clean, dry hands, form the mixture into 12 balls, using a scant 1/4 cup of the mixture for each. Gently immerse these meatballs into the tomato mixture in the cooker. Lock the lid onto the pot.
Optional 1Max Pressure Cooker Press Pressure cook on Max pressure for 10 minutes with the Keep Warm setting off.
Optional 2All Pressure Cookers Press Meat/Stew or Pressure cook (Manual) on High pressure for 12 minutes with the Keep Warm setting off.
When the machine has finished cooking, turn it off and let its pressure return to normal naturally, about 25 minutes. Unlatch the lid and open the pot. Serve the meatballs in bowls with lots of the sauce.