Do you think pastrami on a roll with mustard and pickles is the ultimate deli delight? How do I make it in my kitchen? I think I need to start with thinly slicing the onions and cook it in a small amount of butter over the medium heat until they are nicely browned. What do I do next? How do I proceed from here? What else will I be needing other than the rye bread, butter, spicy brown, the deli mustard, the sliced and the caramelized onions, and a lots of thin sliced pastrami?