I've noticed it last year already, and I'm so glad it's still here this year! What catches your eyes in this patisserie is the poop-shaped cake! Like many asians, I've had a fascination for poop-shaped things since young (I used to draw a poop to sign). And because of my name, all my closest friends call me "kk" (pronounced kaka, caca), which also means "poop" in French. I know it's not really glamourous but I like it. :D
"Petit Caca" is only 3,800 wons! The "Grand Caca" is available at 20,000 wons. I haven't tasted everything yet but they also have Wasabi Ice Cream (yukk, I tried it in Japan, it tastes horrible!) and other original creations. Ah, they also have macarons!
What about taste? I didn't expect anything special and cakes are often prettier than they taste here so I was surprised it tasted pretty good! Lot of cream but there is a layer of fruits "paste" so it's not too "heavy". I couldn't finish it in one go by myself. It should be enough for two small eaters. :) If you're looking for unexpensive patisseries in Hongdae, I recommend it!
How to get there? Hongdae exit 5 (or 9 now), go to the main street leading to Hongik University, go past KB bank and you'll see an Haagen Dazs shop, and some kind of galleria, go to the first floor, le Petit Four is near! :)