Preheat your oven to 180c.
In your Dutch Oven place your onions, garlic, olive oil and mustard and saute over a medium heat for 5 minutes.
Season the skins of your chicken thighs with salt and pepper and place in the dish with the skin facing down. Allow them to brown and go crispy for 5 minutes and while this is cooking, finish preparing your vegetables.
Dice your carrots, chop your new potatoes into quarters, chop your tomatoes into small chunks and slice your black olives in half removing the stones as you go.
When the chicken skin has got a lovely colour to it and created some lovely chicken juices in the bottom of your dish, remove and put to one side.
Place everything else (including the seasoning) into the Dutch Oven and mix well so that the herbs are spread around the dish.
Cook for a further 5 minutes on the hob.
Add the chicken thighs on top and sprinkle with salt and pepper. Cook for 1 hour on a 180c heat.
Serve.