After thoroughly washing your chicken, pat to dry. Place in cast iron skillet breast side up. Spoon dijon mustard and butter onto the chicken. Sprinkle a handful of fresh chopped rosemary, about 4 sprigs of thyme, freshly cracked black pepper, and a generous amount of salt over the chicken. Squeeze the juice of 1/2 a lemon over top (being careful not to lose the seeds).
Using your hands, massage all ingredients over the chicken. Flip over and repeat (adding more rosemary, thyme, salt and black pepper, as needed, and squeezing the other 1/2 of your lemon). You should have a generous and even coating of all the ingredients over the chicken.
Flip back over, so the chicken is breast side up in the cast iron skillet. Stuff the chicken cavity with a handful of sprigs of both rosemary and thyme for extra flavour. Place aside.
Prepare your vegetables (you can use any other root vegetables that you like) by peeling and chopping them. Try to chop everything to a consistent size, so all of your veggies roast evenly.
Add veggies to a large bowl and season with salt, black pepper, rosemary, thyme, and extra virgin olive oil. Toss vegetables so they are coated evenly.
Add vegetables to the same cast iron skillet as your seasoned chicken.
Place cast iron skillet in an oven pre-heated to 425°F and let it roast for 15 minutes. Then reduce to 350°F and let roast for 1 hour. There is no need to flip your chicken over. But as oven temperatures vary, check on your chicken after 40 minutes.
If you have a thermometer (which is not necessary for this recipe), chicken should be cooked to an internal temperature of 165°F. Remove from the oven and let chicken rest for 10-15 minutes. Note that the chicken will continue to rise in internal temperature slightly as it rests.
Serve and enjoy!