A 4-week old first-born, pre-term boy admitted to your dept. 3 days ago. Chief complaint was Vomiting which was projectile without bile in it, and follows each feeding, and the baby is hungry and eager to eat again after he vomits. The baby is dehydrated and has visible gastric peristaltic waves and a palpable "Olive sized" mass in the RUQ. What is the surgery of choice?