To prepare the dried beans, cover with double their weight in water and add the bicarb. Leave to soak for a few hours or overnight. Drain and place the beans in a large saucepan with plenty of water. Bring to the boil, reduce the heat to low and simmer for at least 30 minutes until tender but not mooshy.
Drain well. If the beans are old, they may seem to take forever to soften, so you may need to add more water to the pan. Large beans will obviously take longer than smaller ones. Don’t add any salt to the pan or the beans will never soften.
Heat some of the oil in a large frying or paella pan over medium–high heat, then add just enough of the beans to cover the base of the pan. (You will have to do this in batches as you don’t want to stew the beans.) Cook, stirring, for a minute or two until both sides of the beans are nicely golden. Repeat with the remaining oil and beans.
When you’re on the final batch, toss in the spring onion, garlic, lemon zest, cavolo nero or kale and chilli, if using, and sauté for a minute. Put the rest of the beans back into the pan and season.
Mix in the dill and feta and drizzle with the lemon juice and extra olive oil. Serve in the pan.