Put the chicken thighs in a saucepan, cover with water, bring to the boil and simmer for 20 minutes or until cooked.
Remove chicken skin and shred the meat from the bones, returning the meat to the water in the pan along with the garlic and onion.
Bring mixture to the boil. Break the spaghetti into 1-2cm long pieces and add to the pan. Add the chicken stock cube (you can add a second for a really rich flavour).
Reduce heat and simmer for roughly 30 minutes. You want the spaghetti pieces to really soften and swell, that's what makes them 'noodley'. Season with a little salt, pepper and whatever else you feel like (some mixed herbs, a bit of thyme, etc.).
Slowly add the instant mash mixture and stir in to thicken the water. You can add as little or as much as you like here, this doesn't change the flavour at all just thickens the soup.
Serve. Warm buttered bread goes perfectly with this soup.