What did I just eat?

I forgot to take a picture of it, but it was this nut/fruit looking thing the size of a softball and cut into quarters. The inside was light brown and custard like, then there was a half inch layer of this yellow substance with the outside looking hard and brown but it was soft biting into it. It was really tasty, but I can't figure out what I just ate.

I bought it this morning at a market in Phra Khanong.