What do I have to eat to get fat?

Alright, I'm 15, 6' 3", 155 lbs. so basically really skinny. I have barely any body fat, only muscle, and I was wondering how could I possibly gain FAT. I eat a lot but I only grow in length and not width so if you could suggest some really greasy foods or some special granola bars that could help me get fat, I would really appreciate it. I am unsatisfied with being skinny and will eat LARD if I have to!