Preparation
1 In a sealable bag, combine the red onions, olive oil, mustard, sage, lemon juice, and some salt and black pepper. Mix together well, then add the chicken pieces. Seal the bag and squash with your hands to coat the chicken in the marinade. Place in the fridge for four hours, or overnight if possible.
2 Before cooking, remove the bag from the fridge and allow the chicken to come to room temperature in its marinade. Preheat the oven to 220˚C/200˚C fan/gas mark 7.
3 Arrange the chicken pieces in a large roasting tin, skin-side up. Add the sausages and baby potatoes and squeeze in the marinade from the bag. Toss everything together and drizzle over a little extra olive oil to coat, if necessary.
4 Place in the oven and cook for one hour and 15 minutes, turning the sausages halfway through. Ensure the chicken is cooked throughout before serving.