Snap off the stem ends of the green beans, or cut them off in a big bunch with a knife.
Heat a pan over a medium heat and add the butter. (It helps to use a pan with a light-colored bottom so you can keep track of the color.) Swirl the pan occasionally to be sure the butter is cooking evenly. As the butter melts, it will begin to foam. The color will progress from lemony-yellow to golden-tan to, finally, a toasty-brown.
Once you smell that nutty aroma, add the green beans and saute for 3 to 4 minutes. Add some lemon juice and salt and pepper, then transfer to a platter in batches with tongs.