Preheat the oven to 200°C/180°C fan/400°F/gas mark 6.

Melt the butter in a medium-sized ovenproof saucepan or casserole dish over a medium–high heat. Add the onion and season with salt and pepper. Cover and cook for 5 minutes, stirring once or twice, until the onions are softened.

Remove the lid and add the thyme. Continue to cook for another 10–15 minutes. As they cook and browned bits appear, add a tablespoon or so of water and stir to combine. Once evaporated, add another tablespoon and repeat; this prevents the onions from burning and speeds the process up. You want them to be jammy and a deep golden brown. (If you can caramelise the onions for even longer, go for it: the darker their colour, the sweeter their flavour.)

Next, add the vinegar and stir until evaporated, then add the beans with their bean or veg or chicken stock. Season to taste and bring to the boil for a minute. If using canned beans, you may need to add more salt; bring to a simmer and cook for a further 6–8 minutes to allow the beans to soften.

Reduce the heat slightly, then sprinkle the cheese evenly over the top, followed by the breadcrumbs (if using), especially around the edges (this will give you delicious crispy bits).

Transfer to the oven and bake for roughly 8–10 minutes until the cheese has melted and browned in places. If the top is not as toasted as you’d like, bake for another minute or two. Serve and tuck in.