Rinse chicken with water, inside and out, then pat dry with paper towels.
Place the chicken breast side down on a board or flat work surface.
Next, cut both sides of the backbone of the chicken with kitchen shears; starting at the thigh end, working your way up to the neck. Remove the backbone, and save for homemade chicken stock.
Grab hold of both sides of the chicken, and open like you would a book. Turn the breast side up.
Push down on each side of breast with your hands until you hear it cracking. Then flatten the chicken.
If desired, remove the wishbone. It makes it easier to carve the whole breast in a single piece.
Rub inside and out of the chicken with salt. Set aside.
In a small bowl, combine oil or butter with the spice blend (thyme, oregano, garlic powder, onion powder, ground black or white pepper, and cayenne pepper). Add enough oil so there is enough for basting.
Let this mixture sit for a little bit - about 5 minutes.
Generously rub the chicken inside out with the spice blend, then refrigerate until ready to cook.
Mix together the potatoes with the blackened spice blend mixture in a bowl. Lightly salt and set aside.
When ready to bake, roast the chicken on top of a cookie rack; chicken on top and potatoes below.
Roast at 400 degrees F until the skin is crisp and an instant-read thermometer inserted into the thickest part of the breast reads 165 degrees F, about 35- 45 minutes.
Let it stand 5-10 minutes before cutting each chicken into quarters or to desired pieces.