Preheat oven 400ยบ F
Cut chicken along the backside, removing spine. Flatten and lay on top of sheet pan.
In a small bowl, mix together apricot jam, mustard, brown sugar, olive oil, orange juice, salt and pepper.
Spread around three-quarters of the seasoning mixture on top of and under the skin of the chicken; reserve one-quarter.
Spread potatoes on one side of the pan, Brussels sprouts on the other. Drizzle potatoes and Brussels sprouts with olive oil, salt and pepper. Add whole, unpeeled garlic cloves to the tray, alongside the potatoes and Brussels sprouts.
After 30 minutes, check on Brussels sprouts and, if caramelized to your liking, remove and set aside. Toss potatoes to ensure even cooking and place back into oven for another 25-30 minutes.
Remove from oven and spread remaining seasoning on top of chicken. Cut chicken into quarters and serve immediately.