I was fortunate enough to find this shop back in 2010 when it openned, and it is still as great as ever. I remember going there soon after it openned and ordering the ham and liver patte sandwich straight off. It was literally love from the first bite and rivals anything I've had in Seattle.
Here is a picture of my order today - I add avocado on as well which adds to all the flavors sensations.
I've gotten to know the owner over the years and the shop is a complete hole in the wall with just a few bench seats out front. Nowadays it's almost always packed. The walls inside are litered with magazine and details about tv shows that have covered the shop before. But even though it's crowed, they still push them out at a steady pace. And you can call to pre-order by phone but they won't pick up if it's too busy.
You just step in the door of the shop and there is just enough space to place your order through the vending machine to pay for the sandwich and sides you want. You just had the print out slips to them. They ask for a name. The vending machine is in Japanese but you can ask them. Or if someone else standing around that speaks English. The vending machine saves them time from handling the money, so the 3 to 4 gals behind the counter can just keep their sandwich asembly line going.
The owner really knows her product well and makes everything in the shop. The ham on the sandwich is actually two types of vietnamese pork rolls and one has peppercorns that pop with surprising flavor burst when eating the sandwich. The radish and carrots are pickled and then adding cilantro (Coriander) to mix just finishes all off perfectly. The bake the bread rolls as well as other rolls that they have on sale. An amazing feat in such a small space.
They also have other sandwiches and I've tried a few. On any other day, I'd would walk away happy but knowing they have a gem like the ham & liver patte on the menu - it's a must have in my mind.
And the other great thing is it's cheap. The cost is 550 yen ($5.50 usd) for the full or 300 yen ($3 usd) for a small. But go for the full for sure.
If you bring it home, I suggest putting it in a toaster oven on medium heat for a few minutes. It crisps up the bread and adds another crunchy element to the party in your mouth.
So if you are ever in Tokyo and want a great bahn mi, you just head to Takadonobaba station and it's just one block away on the back street. Here is the link to site on tabelog which is kind of the yelp of Japan for restaurants.
http://tabelog.com/en/tokyo/A1305/A130503/13103176/
Shop info:
Banh Mi ☆ Sandwich (バインミー☆サンドイッチ)
4-9-18 Takadanobaba Shinjuku Tokyo
東京都 新宿区 高田馬場 4-9-18 畔上セブンビル 1F
03-5937-4547 (probably Japanese only - sorry I haven't asked if they speak English or not)