Set your oven to 180 degrees C.

Start with prepping the muslin bag of spices by simply putting all the herbs and spices (except tarragon) and the shallot + tie it up with some string. Set aside

Add beans and their liquid to a medium sized saucepan. Pour over half of the chicken or veg stock, add parmesan rinds and the little bag of spices. Let it all simmer on a low heat whilst you start the leeks.

Trim the leeks and peel off any dry layers and cut in 12cm batons. Line an ovenproof dish and put the leeks on top with the butter and thyme sprigs. Pour over the remaning stock and season with salt and pepper. Cover the leeks with one layer of parchment paper just as a tight lid. This way the leek with steam in it’s own juices.

Check the leeks after 25 minutes, you want them to be soft but not falling apart completely. If not there yet just give them another five minutes.

By now the beans should be braising away nicely and the liquid reduced. Remove the spice bag and give the beans a little taste. Season to taste, add a squeeze of lemon, grated parmesan and top with the chopped tarragon.

Remove the leeks from the oven. I like to serve the beans in a shallow platter with the leeks on top, grated lemon zest, a good glug of good olive oil + an extra grating of parmesan.