Preheat the oven to 325 degrees F Place the oil in a large skillet set over medium-high heat. Season the pork with salt and pepper. Sear the chops, in batches, until brown on both sides. Set the pork in a large casserole (the one used in this recipe was 10” by 14”).
Reduce the heat under the skillet to medium. Add the leek and garlic cook until tender, about 5 minutes. Mix in the flour and tarragon and cook 2 minutes more. Slowly, while constantly mixing, add the stock. Add the lemon juice and zest and bring to a simmer. Season sauce with salt and pepper, and then pour over the pork. Cover and bake 90 minutes, or until the pork is very tender. Sprinkle pork with sliced green onion and serve.