Place a large bowl of ice water in the sink.

Bring a large pot of salted water to a boil over high heat.

Add green beans and return to boil.

Cook until beans are tender, 3 to 5 minutes.

Using a slotted spoon, quickly transfer green beans to ice water to stop cooking.

Drain and lay out on paper towels to dry. (Can be done up to 3 days in advance to this point. Wrap in damp paper towels, cover with plastic wrap and refrigerate. Bring to room temperature before serving.)

In a large bowl, whisk vinegar, lemon juice, mustard, shallots, 1/4 tsp salt and 1/8 tsp pepper until blended.

Slowly add both oils, whisking constantly until thickened. (Can be made up to 3 days in advance, minus the shallots. Keep chilled in a glass jar with a tight-fitting lid. Add shallots right before using.)

Just prior to serving, toss beans with vinaigrette and add shallots.

Serve at room temperature.