Heat the oven and an appropriately-sized roasting tray to 425 degrees F.
Wash chicken inside and out and pat dry with paper toweling. Using your
fingers, part the breast skin from the breast meat. It's important to try
to push your hand gently down the breast, being careful not to rip the skin.
With a peeler, remove and chop the fragrant yellow skin of the lemon, keeping
the peeled lemon to one side.
Chop prosciutto and add to the bowl with the lemon skin, garlic and thyme.
Season, with salt and pepper and then mix it all into the butter. Push this
into the space you have made between the meat and the skin - rub and massage
any that's left over in and around the bird. Slash the thigh meat to allow
the heat to penetrate a little more, which makes it taste better. Cut the peeled
lemon in half and push it into the cavity.
Put chicken in the hot roasting tray and roast in the preheated oven for
While the chicken is cooking, parboil the potatoes in salted water for 10
minutes and drain.
Cut the celeriac into irregular chunks around the same size as the potatoes.
Remove the chicken from the oven, by which time the tasty butter will have
melted, flavored and cooked out of the chicken into the bottom of the tray,
awaiting your potatoes and celeriac.
Put a fork into the cavity of the chicken and lift it off of the tray for
20 seconds while tossing and coating the vegetables in the butter.
Put the chicken back on top of the vegetables and cook for about 40 minutes.
Let stand for 10 minutes.
When the meat and vegetables have been removed, a little light gravy can
be made in the tray with a splash of wine and stock, a little simmering and