Put the drained beans in a large pot with enough water to cover by 3 in/7.5cm and bring to a boil. Reduce the heat to medium-low and simmer the beans al dente, about 1 hour.

Meanwhile put the spinach in a large colander and sprinkle lightly with salt. With the palm of one hand, rub the spinach against the holes of the colander, almost in a kneading motion, so that the greens exude liquid. Do this for 10 minutes, and then put a plate over the greens and a weight on top of the plate (such as a large can of tomatoes) and leave to drain for 1 hour.

Heat the 2 tbsp olive oil in a medium frying pan over medium heat and cook the leek and onions, stirring, until wilted, about 10 minutes. Preheat the oven to 350 F/175 C

Combine the drained greens with the cooked onions, the herbs, and 1 cup/150 g of the feta in a large bowl. Drain the beans, reserving 4 cups/960 ml of the cooking liquid and add to the bowl. Add 1 cup/175 g of the tomatoes and toss to combine. Taste and add salt, if desired, and some pepper.

Put the beans-and-greens mixture in a large ovenproof casserole or baking dish and mix in ¼ cup/60 ml olive oil and 2 cups/480 ml of the bean cooking liquid. Spread the remaining 1 cup/175 g tomatoes over the beans and sprinkle the remaining ½ cup/75 g of feta and the bread crumbs on top. Drizzle the remaining ¼ cup/60 ml olive oil over the surface and bake, covered with parchment then aluminum foil, until the beans are very creamy and soft, but not disintegrating. Depending on the age and condition of the dried beans, this could take anywhere from 1 to 2 ½ hours. Add more liquid to the pan during cooking if necessary to keep the beans from drying out. Remove the paper and foil about 30 - 45 minutes before removing the beans from the oven, so that the surface caramelizes and chars slightly. Serve hot or at room temperature, accompanied by pita bread.