1. PREPARE the sauce in a medium bowl by whisking the Pioneer Brown Gravy Mix and water until thoroughly incorporated. Set aside.
2. PLACE the bread crumbs, onion, salt, black pepper, and ground nutmeg in a medium bowl and stir well to combine.
3. PLACE the ground beef in a large bowl and incorporate the bread crumb mixture into the meat. Do not overmix.
4. PLACE the egg, milk, and Worcestershire sauce in a small bowl and whisk until thoroughly incorporated.
5. POUR the egg and milk mixture over the ground beef and incorporate into the meat. Do not overmix.
6. SHAPE the meatballs into golf-ball-sized pieces, and place into the Instapot.
7. POUR the sauce mixture over the meatballs.
8. PRESSURE COOK on HIGH for 10 minutes.
9. ADD sour cream to the sauce and stir until thoroughly incorporated.
10. SERVE over prepared egg noodles.