3 Tablespoons butter, divided use
6 shallots, peeled and thinly sliced into rings
Coarse salt and ground pepper
In a medium saucepan with a tight-fitting lid, melt 2 Tablespoons butter over medium heat; swirl to coat bottom of pan.
Add shallots; cover.
Reduce heat to medium-low; cook, stirring occasionally, until golden brown, 15 to 20 minutes.
Meanwhile, in a large pot of boiling salted water, cook green beans until fork-tender, 4 to 6 minutes.
Drain; return to pot.
Toss with remaining Tablespoon butter.
Season with salt and pepper.
Transfer green beans to a serving dish; top with caramelized shallots.