Put the spinach in a sieve then pour boiling water over it. When cooled, squeeze the water out with your hands, then chop finely.
Drain the beans and coarsely mash with a fork.
Thinly slice the leeks, then gently cook in the oil until soft. Let it cool.
Combine everything together in a large bowl, season to taste with salt and pepper. Mix well.
Form 4 large or 6 small balls from the mixture. Press these slightly between your palms - then put them on a plate and rest in the refrigerator - for about 15-20 minutes - if time allows.
Pan-fry the patties in hot oil on each side until golden brown (about 3 minutes) - or put them under the grill in the oven, turning over once.
Serve them in a bun or wrap with salad and condiments.