Heat 2 tbsps of the olive oil in a very large frying pan over a medium heat. Toss in the rosemary and stir around for a couple of minutes then remove and discard.
Add the garlic and fry for a minute, stirring often. Now put the butter, parmesan, beans ( including reserved liquid) , anchovies and three quarters of the parsley into the pan.
Stir everything together, mashing about a quarter of the beans to thicken the juices. Reduce the heat to low to medium and gently cook for about six minutes, stirring occasionally, until the contents of the pan look a thick gloopy mess.
Meanwhile, cut the “heels” off the ciabatta and discard them. Slice the loaf in half horizontally then cut each half in two to make four pieces. Toast the ciabbatta then immediately drizzle each piece with a mixture of the reserved anchovy oil and the remaining 2 tbsps of olive oil.
Stir the basil and the remaining parsley into the bean mixture and season generously with black pepper and sea salt to taste. Spoon the beans on top of the ciabatta and serve immediately.