Trim the beans and remove the strings if necessary.
Place a couple of centimetres of water in the bottom of the pan your steamer fits in and bring to the boil. Steam the beans for 3-5 minutes, depending on how tender you like them.
Transfer the beans to a bowl and toss with 1 tablespoon butter and salt and pepper. Add the lemon juice and toss again, then finish with the last tablespoon butter. Add more salt and pepper if necessary. Serve!