Make a “roux” with the oil, potato starch, and garlic powder: Heat the oil over a medium-high flame for about 30 seconds; add the potato starch and garlic powder, and mix with a wooden spoon until it’s light-medium brown and combined well.Add the spinach to the pot and mix on medium flame until it’s combined with the roux. Add the chicken stock, salt, and pepper, and mix it until well combined. Let it cook for 5 more minutes over medium flame until very creamy and the spinach is cooked through.