Like I said, I normally eat Bak Kut Teh at night (especially after clubbing :-p) There are many famous Bak Kut Teh around Penang. But the one that I always go and like most is the one at Dato Keramat, Lao Fu Zhi Bak Kut Teh. Not because the owner is my friend but their Bak Kut Teh is Bak Kut Teh. (What statement is that?) What I mean is they putting in the real stuff, herb and others to make the Bak Kut Teh. Not like the prepack Bak Kut Teh you can get in hypermarket.
This Lao Fu Zhi Bak Kut Teh is 老招牌, it been around for a few decades. If you drive too fast along Jalan Dato Keramat, you might miss it. In the street view, it found at the left side after curve road of Jalan Dato Keramat into Jalan Ayer Itam. Hard to explain if you're from outstation, use the GPS coordinate: 5.413498,100.312117 and see the map:
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It open from dinnertime until the next day morning. 1am, you can't sleep. You go there, still open. 2am, you hungry, you go there, still open. 3am, you drunk, you go there, it still open.
It just cost RM5, not sure it is a friend's price or it is that cheap. Look at the ingredients, more than the Raja Uda Yam Rice and better than having Nasi Kandar at Mamak Stall.