In a roasting tray, combine the garlic, spices, sugar and 1 tbsp olive oil. Season, add the chicken thighs and turn to coat. Cover then marinate for 15 minutes or in the fridge overnight.
Preheat the oven to 180°C, gas mark 4. Add the potatoes to the tray, tucking them among the chicken. Drizzle with the remaining oil. Roast for 25-30 minutes, or until the chicken is cooked through and the potatoes are tender. Add the plum quarters for the last 10 minutes’ cooking.
Garnish the traybake with the micro coriander and serve at the table.