In a deep saucepan large enough to hold all of the broccoli rabe, heat the olive oil over medium heat. Chop the garlic coarsely and add it to the pan, along with the pepper flakes and anchovies. Cook 3 to 5 minutes, until the garlic begins to soften.
While the garlic is cooking, wash the broccoli rabe thoroughly. Add it to the saucepan with the water still clinging to its leaves. Cover the pan tightly and cook the broccoli rabe for 20 to 30 minutes, until it is very tender and just a few spoonfuls of water remain. When the broccoli is tender, add to the sauce with a little salt and the olives. Toss and serve hot.