I found this by accident as it was on the walk back to my hotel. It doesn't look much from the outside, a bit basic and café-ish. The menu looked reasonable though, and it was the Christmas period so there were fewer places open.
I went there the next night (Christmas eve) and there was only one diner in there. It is only a small restaurant , maybe half a dozen tables. The staff member who greeted me was very friendly and took me to my table. I ordered the dhal takhaar, which came with rice, a garlic naan, and a bottle of beer. Many vegetarian curries I've had tend to be a bit bland, but this was delicious. The garlic naan had a plenty of garlic which I love, although it was not too overpowering. Even though I was full before the end, I finished it as it was too nice to waste! The whole lot came to about 13 Euros which was very reasonable indeed. While there another customer came in and didn't want rice, asked if she could swap it for a naan bread, which he did obligingly. When I paid he was very friendly, wishing me a merry Christmas. I would definitely go back there again if I ever go to Amsterdam. It's worth the 10 min walk out of town (or you could get a tram to around the corner)