Blanch the string beans in a large pot of boiling salted water for 1 1/2 minutes only. Drain immediately and immerse in a bowl of ice water.
Heat the butter and oil in a very large saute pan (12-inch diameter) or large pot and saute the shallots on medium heat for 5 to 10 minutes, tossing occasionally, until lightly browned. Drain the string beans and add to the shallots with 1/2 teaspoon salt and the pepper, tossing well. Heat only until the beans are hot.
If you're using regular string beans, blanch them for about 3 minutes, until they're crisp-tender.
