Trim the ends off the beans if they're not already cleaned.
Bring a pot of salted water to a boil and blanch the beans for 1 1/2 minutes. (If you're using regular green beans, blanch for 3 minutes.) Drain right away and put the beans in a bowl of ice water. You can do this part ahead of time.
Heat the butter and oil in a large skillet and saute the diced shallots over medium heat for 5-10 minutes, stirring periodically. You want them lightly browned.
Drain the beans and add them back to the pan along with the salt and pepper. Stir and heat just until the beans are hot, then serve.