Slide 2 fingers between breast skin and meat on chicken to make pockets. Turn chicken over and loosen thigh skin the same way. Mix salt and pepper; evenly rub 1/4 tsp. over meat in each pocket and the rest over outside of bird. Put chicken on a rack in a rimmed pan, very loosely cover with plastic wrap, and chill 2 days.
Pat chicken dry inside and out. Make seasoning, if using, and add to chicken as directed. Oil chicken (for plain or French Herb). Set chicken breast-up on a V-shaped rack in a 12- by 17-in. roasting pan; tuck wing tips under if you like. Let stand at room temperature 30 minutes. Meanwhile, preheat oven to 475°.
Roast chicken until an instant-read thermometer inserted horizontally through thickest part of breast reaches 160°, 30 to 45 minutes for a smaller bird or 45 to 50 minutes for a larger one. Transfer chicken to a warm platter and let stand in a warm place about 10 minutes.
*To find small (uncooked) chickens, try markets that roast rotisserie birds (which are small) on-site.
Note: Nutritional analysis is per serving plain chicken.