From Katoshka which has booths in both sections of Geylang Serai Bazaar:

I saw a queue at Katoshka’s booths every time I visited this year except for when they were out of fries. Waited for about 15 minutes to order, but we were quickly served a cup of hot fries drenched in their special cheese sauce. Although there are other sauces and even chicken cutlet available on the menu, this seems to be the only dish that everyone orders and I can see why. The fries are awesome. They’re crispy on the outside and well-seasoned. I love the cheese sauce here as well, which is creamy but not too thick. It’s also cheesy, but never gets jelak because there’s a slight sour aftertaste that isn’t unpleasant. In fact, you just want more of it after each bite. I probably wouldn’t queue more than 10 minutes for a second taste of this, but it’s definitely worth a try at least because those are some damn good fries.