Rinse meat to remove residue and pat dry with paper towels. Prepare a rub by combining cayenne, paprika, chili powder, fajita seasoning, and Smokey Rotisserie seasoning in a small bowl. Squeeze lemon juice into bowl to make a paste and rub over entire surface of prime rib.
Follow manufacturer's instructions for the smoker. General rule of thumb is to maintain a temperature range of 255 to 300 degrees F (indirect heat), and smoke for 1 to 1 1/2 hours per pound of meat.
Beat heavy cream with an electric beater until stiff peaks form. Squeeze in lemon juice, 1/2 of lemon at a time, and beat in until incorporated. Then gradually beat in horseradish and salt and pepper. Chill for about an hour before serving.
Slice down prime rib and serve with horseradish cream.
2007, Robert Irvine, All Rights Reserved.