Heat the oil in a large, wide-based pan, add the onion and stir-fry on a medium to high heat for five minutes.
Add the garlic and chard stems, then stir-fry for five minutes more.
Add the chard leaves, 750 ml just-boiled water, salt and 150 g of the drained beans, stir well, bring to a boil, then turn down the heat and leave to simmer for 10 minutes.
Take the pan off the heat, leave the soup to cool for five minutes, then stir in the lemon juice and roughly blend with a stick blender.
Alternatively, carefully blend in a food processor, in batches if need be.
While the soup cools, melt the butter in a frying pan on a medium heat and, when it's foaming, add the garlic and aleppo pepper, if using.
Cook for a minute, until the garlic starts to crisp up, then add the remaining 110 g drained beans.
Stir, turn off the heat, then taste and adjust the salt as needed.
Add the yoghurt to the soup pan, whisk it in well, then taste and adjust the seasoning as required.
Transfer to bowls, swirl through a little extra yoghurt, if you wish, top with the crisp garlic butter and beans, and serve at once.
