Service tax liability on free serving of food in restaurant

One question is there relating to food related service,
suppose i have restaurant and i m serving one food say Sandvich and one Sandvich as complementary for which i m not charging anything i.e. free of cost, and i m charging for One Sandvich only, will i have to pay service tax on free Sandvich that i am serving as complementary( as free) ?
Need your advise with proper rules and case law if any