Vendors traditionally boil the banana-leaf-wrapped rolls for 24 to 48 hours straight, which is what caramelizes the peanuts and rice flour into a dense, fudge-like log.
Ground peanuts, rice flour and brown sugar are packed into a banana-leaf roll and boiled for a full day or more, producing a dense, chewy cake that's sliced and sold by vendors — famously hawked through train windows at stops along the east-coast railway into Toamasina.
Sambos
Nem Malgache (Malagasy Spring Rolls)