This food truck sells fries on the go. The only way you can find them would be following them on twitter, check out their website, or just plainly be lucky and bump into them in the streets.
It was a hot day when J and I ordered from this truck, they apparently were stationed at Union Square for maybe an hour and was planning to change locations. Good thing we caught them before they leave. They had over 15 types of sauces on their menu and not only did they have regular potato french fries, but also sweet potato fries. We wanted the combination but they told us they were out of sweet potato. I was quite disappointed but the heat was making it too uncomfortable for me to even care. Eventually, we got our fries and 2 types of sauces.
The two sauces were Vampire Repellent (Roasted Garlic & Nutmeg Aioli) and Dave's Roasted Poblano BBQ Sauce. I personally liked the BBQ sauce a lot more than the Vampire Repellent, I mean it wasn't that bad but the garlic and nutmeg with fries was just too weird for me. They have a heck more sauces that might suit each person.
I probably won't be coming back to the Frying Dutchmen just because I find that Pomme Frites are a heck lot better.
Various Location in NYC