In a bowl, combine the ground beef, bread crumbs, chopped onion, egg, Worcestershire sauce, garlic powder, salt, and pepper. Mix until fully combined, being careful not to overmix.

Roll the meat mixture into approximately 1-inch meatballs and set aside on a plate.

Spray the bottom of your slow cooker with cooking spray or use a slow cooker liner. Place the meatballs in the slow cooker.

In a separate bowl, mix together the beef broth and creamy mushroom soup. Pour this sauce over the meatballs.

Cover and cook on low for about 6 hours, or on high for 3 hours, until the meatballs are cooked through and tender.

About 30 minutes before serving, place the potatoes in a large pot of salted water and bring to a boil. Cook until fork-tender, about 15-20 minutes.

Drain the potatoes, then return them to the pot. Add the milk, butter, and salt, mixing until smooth and creamy.

Once the meatballs are done, serve them over a generous scoop of mashed potatoes, drizzling some of the gravy over the top.