1. Preheat the oven to 160°C, setting the steam bursts to take place every 30 minutes.
2. Grind the rosemary, lemon thyme, salt and garlic into a paste using a pestle and mortar, then mix in the olive oil. Rub the paste all over the chicken.
3. Place in the oven for 1 hour 40 minutes. Once cooked, leave the chicken to rest for 10 minutes.
4. Roughly chop all of the herbs then add to a blender with the Dijon mustard, white wine vinegar and salt. Blend on a low setting. While blending, slowly pour in the olive oil to emulsify.