I know you’re probably thinking, why would I want to cook a casserole in the middle of summer? Well, sometimes when it’s one BBQ after another, a make-ahead meal like a casserole is a welcome change. The flavours in this casserole certainly pack a punch - the lamb is simply delicious and melts in your mouth. The butter beans combined with the zingy lemon and mint notes lift the lamb casserole, making the combination of the two dishes just awesome.
Cut lamb leg into bite-sized chunks, removing any sinew you discover along the way, and set aside.
Heat olive oil in a large casserole pot over a high heat until shimmering. Sauté lamb pieces until golden (in batches so as not to overcrowd the pot), about 3-4 minutes. Remove from pot and set aside. Note: additional extra virgin olive oil may be required for the sautéing of the lamb pieces whilst sautéing in batches.
Add garlic cloves to remaining oil in pot and cook over a medium heat, whilst stirring, until golden, about 3 minutes. Add herbs, tomato paste, and harissa paste and cook over a medium heat, continuing to stir for 1-2 minutes. Add red wine, salt and pepper, then bring to a rapid boil and reduce by two thirds, which will take approximately 8 minutes.
Return sautéed lamb pieces to casserole pot and cover with stock. Bring to a simmer, then cover and cook for 2 hours, checking and adding more stock to keep lamb covered if necessary. The lamb is done when soft to the touch and almost falling apart.
Carefully strain off liquid into a fresh pot, setting lamb aside. Add carrots, then bring sauce to a boil and reduce until ¼ of the cooking liquor remains. Return lamb to cooking liquor, taste and adjust seasoning if necessary with salt and pepper.
For the cannellini beans, cover in cold water and soak overnight (they'll expand, so make sure your bowl is big). Drain and rinse, then transfer to a large pot and cover with 5cm cold water. Bring to the boil, scoop off any foam, then boil for a further 10 minutes.
Scoop foam off again, then add just a little salt (too much salt before they're cooked will harden the skin, as will anything acidic like lemon juice or tomatoes). Simmer gently with the pan lid half on, stirring occasionally, until beans are tender, about 35–40 minutes. Keep an eye on the water level and add more if necessary.
Drain and mix beans together with lemon zest, lemon juice, olive oil, mint leaves, white pepper and grated parmesan, then taste and season with salt. Finally transfer to a serving dish and drizzle over a tablespoon or two of extra virgin olive oil.
Divide lamb and cannellini beans between plates, scatter feta on top and serve.