Bring a large pot of water to the boil.Cut the broccoli into evenly sized florets.Gently add the broccoli to the boiling water and cook for 3-5 minutes, until the broccoli is tender.Drain the broccoli and return it to the warm pot, add the butter, lemon juice and zest, salt and pepper.Blend the broccoli with a stick blender until there are no lumps.Stir through the crumbled feta cheese and serve.