Interesting. It's been years and years since I had any Japanese peanut butter, but a quick search for Japanese recipes indicates that most call for butter/margarine and sugar, but not yolks. Literally, peanuts + butter = (Japanese) peanut butter. It makes me wonder if Japanese peanut butter morphed into a butter-based paste due to a transliteration issue. Although the recipe may seem "weird," it isn't necessarily bad if the results taste good. ← Who said bad? I didn't say bad. It's just that after years of conditioning, I didn't expect peanut butter to actually contain butter. I'm much more open minded than I sound.