Place 1 pound trimmed green beans and 1 cup water in a microwave-safe dish large enough to hold them.
Cover the dish with a microwave-safe plate or microwave-safe cover.
Microwave on high for 6–7 minutes, until the beans are tender when pierced with a fork; if they are not tender, continue microwaving in 1-minute increments until done.
Carefully remove the dish from the microwave and drain off the cooking water.
Stir in 1 tablespoon butter until melted and the beans are coated.
Season with salt and freshly ground black pepper to taste and serve.