Direction :

1. Heat the oven to 450ºF (convection roast if possible). 
2. Thinly slice the shallots. I love using my mandoline for this, but a knife works just fine, too. You need roughly 2 cups. 
3. Place 1/4 cup of the olive oil and the shallots in a skillet (I’ve been using a 9-inch cast iron skillet) and set over high heat. As soon as the oil and the shallots begin to sizzle, give the shallots a stir, then turn the heat to low. Line a plate with a paper towel or cloth dish towel. Cook the shallots for 25 to 30 minutes or more, stirring occasionally until they’ve turned a deep amber hue — be patient here. The shallots will soften first, then slowly begin to caramelize. If you turn up the heat, they’ll burn quickly. Low and slow is the name of the game here. That said, you can turn up the heat here and there if you wish, but if you do, stir continuously. As soon as you walk away from the skillet, turn the heat to low. Once the shallots are caramelized and beginning to crisp, use a slotted spoon or slotted spatula to transfer them to your prepared plate. Season with a generous pink of flaky sea salt. Once they are completely cool, you can transfer them to a storage container. Store at room temperature for 2 to 3 days. 
4. Meanwhile, place the green beans on a rimmed sheet pan (at least 13 x 18 inches). Toss with the remaining 2 tablespoons of olive oil and 1.5 to 2 teaspoons of the kosher salt. If you are sensitive to salt, use 1.5 teaspoons to start. I do not find 2 teaspoons of salt to be too salty here, and I, in fact, finish the green beans with more flaky sea salt to taste (but, as many of you know, I do love salt). If you are using Morton Kosher salt, you’ll want to use half as much: start with 3/4 teaspoon, then season with more to taste after the beans have roasted. And same goes for fine sea salt: use 3/4 teaspoon to start. 
5. Spread the beans in an even layer, then transfer the pan to the oven for 15 minutes (or 10 minutes if using only 1 pound of beans). Remove the pan, stir the beans, then return to the oven for 5 to 10 minutes more or until some of the greens are charred at the edges and all of the greens are crisp-tender. 
6. Remove the pan from the oven and toss with 2 to 3 teaspoons of the vinegar (I use 3 teaspoons). Taste. Add flaky sea salt or more kosher salt to taste. Toss, taste, and adjust with more salt and vinegar to taste. 
7. Transfer the beans to a platter, then top with the caramelized shallots. Serve immediately or at room temperature. I find these delicious at room temperature or even beyond room temperature (as in cold many hours later but not refrigerated cold).