Preheat the oven to 400°F.
To make the stuffing: Crush the fennel seeds in a mortar and pestle and then transfer to a medium-sized bowl. Add the sausage, breadcrumbs, parsley, egg, and chicken broth to the bowl and season with salt and pepper. Using your hands, combine the ingredients until evenly mixed together.
Remove the chicken giblets from the cavity. Rinse the chicken inside and out, and pat dry with paper towels. Stuff the cavity with just enough of the stuffing to fill it, making sure not to overstuff. Tie the chicken legs together with kitchen twine. Rub the butter over the entire surface of the chicken. Drizzle the chicken with the olive oil and season with the salt and pepper.
Place the chicken breast-side up in a roasting pan. Roast, basting the chicken occasionally, until the skin is golden brown all over and the stuffing registers 165°F, about 1 hour, 30 minutes.
Remove the chicken from the oven and allow to rest for 10 minutes before serving.
If you like to have some extra stuffing you can double the stuffing recipe ingredients (except the egg which you should keep at one). Prepare your stuffing as stated in the recipe. Fill the cavity of your chicken and then bake the excess stuffing separately in a buttered oval gratin dish measuring 6.5 inches. Cover the dish with foil and bake for 30 minutes. Remove the foil and bake, uncovered, for another 10 minutes.