The trick with coconut butter, AKA coconut manna, is to run the jar under warm water so it’s nice and soft. The coconut butter separates when cold and the oil comes to the top, so warming it and mixing it back together is essential. If you only scoop out coconut oil, you will have an oily sauce that won’t thicken. You want to make sure you’re scooping out pureed coconut meat, the thick, opaque white mass. That’s what will make the perfect swap for roux.