Preheat the oven to 200°C/fan 180°C/gas 6.
Melt half the butter in a frying pan and sweat the onion with the thyme, bay leaf and ground cloves (if using). Cook for approximately 10 minutes, stirring often, until the onion is golden and totally softened but not coloured or browned.
Add the tomato purée and cook for a minute or two, stirring constantly. If it catches a little, this is good. Add the beans followed by the black treacle, and stir until everything is thoroughly combined.
In a separate small frying pan, fry the bacon pieces until nicely coloured and crisp, then remove, leaving the fat in the pan.
Take a medium ovenproof dish and put half the bean mixture into the bottom. Scatter over half the crispy bacon, then add the remaining beans, followed by the rest of the bacon. Season the tomatoes with a little sea salt, place them on top, dot with half the remaining butter, then put the dish into the oven and cook for 20 minutes, or until bubbling, with the tomatoes beginning to crisp at the edges.
Meanwhile, put the breadcrumbs into the frying pan that the bacon was cooked in and add the rest of the butter, the black pepper and a little more thyme. Stir constantly over a medium heat until the breadcrumbs are golden, and just before they get to this stage, stir in the garlic, making sure it’s distributed through the breadcrumbs, not in one lump.
Take the beans out of the oven and cover them with the breadcrumbs, then put them back into the oven for a further 5 minutes.
Serve immediately, maybe accompanied by buttered curly kale.