Drain and rinse the soaked butter beans. Cook them in a large saucepan of boiling water for 5 minutes, then reduce the heat and simmer gently for about an hour until the beans are tender but not mushy. Drain and refresh them under running cold water.
Heat the olive oil and butter in the base of a tagine or large, heavy-based saucepan over a medium heat, stir in the garlic, onion, chillies, coriander seeds and sugar and cook for 2–3 minutes to let the flavours mingle.
Add the drained butter beans, olives and lemon juice and season with salt and pepper. Cover and cook gently for 10 minutes. Add the tomatoes and thyme, re-cover and cook gently for a further 5–10 minutes. Garnish with the flat leaf parsley and serve with chunks of crusty bread, if liked.