Bring a medium pot of water to a boil. Add the salt and return to a boil.
Add the green beans and continue to boil on high for about two minutes until the beans look cooked but are still bright. Test one if you're not sure.
Drain the beans in a colander. Quickly pour cold water over them to stop the cooking. Let them drain completely, for at least a few minutes.
Meanwhile, melt the butter in a frying pan over medium-low heat. Add the green beans and cook for 2-3 minutes, stirring a few times, till the beans are warmed through and the butter is coating them evenly.