Wash the heads of escarole carefully, leaving them whole and discard any damaged outer leaves.
Cut up the olives into thin rings and put them into a small bowl. Chop up the anchovy fillets and add them to the olives. Add the whole capers and a tablespoon of olive oil, and mix through.
Gently open out the heads of escarole a little and divide the olive mixture between the four, spooning it into the centre of each and also between some leaves. Close up the escarole and tie up securely with kitchen string towards their centre, so the filling doesn’t come out during cooking.
Put the garlic, chilli, the remaining olive oil and the butter into a large saucepan and heat up. Add the escarole bundles, cover the saucepan with a lid, and simmer gently for 15-20 minutes. Remove the lid, turn the bundles over and continue cooking, uncovered, for another 5-10 minutes. There should be very little liquid in the pan. If it looks too dry during the cooking process, add a few drops of water to prevent the escarole from sticking. Serve them whole, or carefully divide the bundles vertically into halves.