Place the chicken into the roasting pot and loosen the skin over the breasts.
Using a magic whisk (or slender silicone spatula), scoop up a small amount of the rosemary mustard paste and slide it underneath the skin, spreading it directly onto the breast meat. Repeat this process until the breast meat on both sides is evenly coated, but at least a tablespoon of the paste remains for the outside.
Spread the remaining tablespoon of rosemary mustard paste over the top of the chicken. Then cover the pot and place it in the oven. Set a timer for one hour, and while the chicken begins roasting, prepare the root vegetables.
Peel all of the vegetables (except the small potatoes). Then chop the carrots, parsnips, yam, and red onion into large pieces roughly equal in size.
Place the vegetables on a baking sheet. Add the reserved half of the rosemary mustard paste, again making sure at least a tablespoon remains for later use in the jus. Toss the vegetables with the paste until evenly coated.
After the chicken has roasted for an hour, remove the lid from the pot. Place the vegetables in the oven as well and set a timer for another 45 minutes. When the chicken has had its one hour and 45 minutes in the oven, test it for doneness. (The juices should run clear and the drumsticks should move easily.)