1. Place the diced potatoes in a large pot. Add enough water to cover them completely.
2. Bring to a boil over medium-high heat, then reduce to simmer. Cook until the potatoes are tender, about 10-15 minutes.
3. In a separate pan, sauté the diced onions until translucent. If using chicken tenderloin, add it to the onions and cook until it’s no longer pink.
4. Drain the potatoes, reserving a cup of the cooking water. Return the potatoes to the pot.
5. Dissolve the chicken bouillon cubes in the reserved water, then pour it over the potatoes.
6. Add the sautéed onions (and chicken if using) to the pot along with the milk.
7. In a small bowl, whisk the flour with a small amount of water to create a smooth paste. Add this to the soup to thicken it.
8. Stir in the dried parsley and garlic powder. Continue cooking over low heat, stirring occasionally, until the soup is thick and creamy.
9. Serve hot and enjoy the comforting flavors.