Fill and boil your kettle. Trim the roots and top 3cm off the leeks. Halve them, rinse out any grit and finely slice them. Put a large pan on a medium heat and add 1 tbsp olive oil and the leeks. Add 1 tsp fennel seeds and season with a pinch of salt and pepper. Fry, stirring often, for 10 mins till the leeks have softened and picked up a little colour.

While the leeks fry, peel and grate or crush the garlic. Pick the thyme leaves off their sprigs. Halve the cabbage and set one half aside for another day. Halve the remaining cabbage half and slice out the thick middle cores. Thinly slice the leaves.

Stir the garlic, the thyme leaves and the cabbage into the pan. Fry, stirring, for 5 mins till the cabbage starts to soften.

While the cabbage fries, drain and rinse the butter beans. Once the cabbage has started to wilt, add the butter beans. Crumble in the stock cube and pour in 1 ltrboiling water. Bring to the boil, then turn the heat down and simmer for 10 mins till the veg are very tender. Don't cover the pan - this helps keep the cabbage green.

Take the soup off the heat and blend it with a hand-held blender in the pan, or transfer to a blender to blitz till smooth. Taste and add a pinch of salt and pepper if you think it needs it. Ladle the soup into warm bowls, drizzle over the pesto and serve.