1. In a frying pan, add the oil (1 tbsp ) over medium heat and add garlic, stir-fry until they turn a nice brown color. Add onion, button mushroom and beef stock cube, then stir-fry until the onion become wilted. Let it cool and set aside.
2. In a large bowl, combine minced beef, all the seasoning ingredients (egg, salt, garlic powder, potato starch, panko/bread crumbs and onion mixture and mix well with a wood spatula or hand.
3. Shape the mixture into 2.5 to 3cm size meatballs and place them in pan gently. Fry meatballs in batches until it forms. No need to bake completely as you cook them in a slow cooker.
4. Add all meatballs and the sauce ingredients into the slow cooker. Cover and cook on medium for 2 hours.