Preheat the oven to 190°C. Arrange the duck legs on a lined baking tray and season generously. Bake for 20 minutes. Meanwhile, heat the olive oil in a large casserole dish over a medium-high heat. Add the chorizo and fry for 1 minute.
Add the onion and garlic and reduce the heat a little. Cook for 4-5 minutes, stirring regularly, until the vegetables start to soften. Add the stock, tomato purée and bay leaf, stir well and set to one side. Remove the duck legs after 20 minutes and add to the casserole dish.
Cook gently over a low heat for 45 minutes, then add the beans and cook for a further 25-30 minutes. 10 minutes before the casserole part of the dish is ready, heat the grill to hot and grill the sausages, turning occasionally to cook evenly.
Adjust the seasoning of the casserole after the sausages are cooked through and discard the bay leaf. Spoon onto serving plates and garnish with a sausage and a sprig of thyme before serving.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.