Step 1Heat the oven to 450 degrees. Rinse the capon inside and out and pat dry. Season the cavity generously with salt and pepper to taste.
Step 2Using your fingers, carefully lift and separate the skin from the breast and legs to form a pocket, being very careful not to tear the skin. Push dabs of the truffle butter deep into the pocket, smoothing the skin from the outside to disperse the butter evenly. Season the skin generously with salt and pepper.
Step 3Place the capon on a rack in a deep roasting pan. Roast until an instant-read thermometer inserted into the thickest part of the breast reads 165 degrees, or until the juices run clear, 1 1/4 to 1 1/2 hours. Do not baste.
Step 4Remove the capon from the oven and tent loosely with aluminum foil. Let stand 30 minutes before carving (make sure each slice has skin attached for best flavor).