Preheat the oven to 190°C fan-forced.
Pat the chicken Marylands dry with paper towel and season generously with salt and pepper.
Heat the olive oil in a large ovenproof roasting dish or frying pan over medium-high heat.
Place the chicken skin-side down and cook for 8–10 minutes until the skin is deeply golden and crisp.
Turn the chicken and cook for a further 2 minutes.
Scatter the grapes, shallots and garlic around the chicken.
In a small jug, whisk together the white wine, chicken stock and Dijon mustard. Pour into the tray around the chicken.
Dot the butter around the tray and scatter over the chopped tarragon.
Transfer to the oven and roast for 40 minutes, or until the chicken reaches 75°C in the thickest part of the thigh.
Remove from the oven and rest for 5 minutes.
Spoon the pan juices over the chicken and scatter with the remaining tarragon before serving.