Cooking beef brisket in the slow cooker makes it really tender and a creamy bean mash is the perfect accompaniment.
Season the brisket joint generously with with salt and freshly ground black pepper.
Sprinkle the sliced onions and bay leaves over the bottom of the slow cooker, top with the brisket and pour over the stout.
Cook on low for 8-10 hours.
For the cannellini bean mash, heat the butter in a frying pan and cook the leeks over a very gentle heat for 20 minutes, or until completely softened.
Stir in the garlic and thyme leaves and season with salt and freshly ground black pepper.
Blend the beans, leek mixture, crème fraîche and parsley in a food processor to a purée.
Return the mash to the frying pan and warm through. Season, to taste, with salt and freshly ground black pepper.
To serve, spoon the mash onto serving plates. Carve the brisket into slices and place alongside. Spoon over a little of the cooking liquid from the slow cooker.