Heat 2 tbsp oil in a large flameproof casserole. Fry the onion for 8-10 mins over a low heat so it starts to soften and caramelise. Add the celery and cook for a further 5-10 mins until softened. Add the tomato purée and cook for 2 mins, then add the tomatoes, sugar, mustard, thyme, carrots and 400ml water, and bring to the boil. Cook, uncovered, over a low heat for 15 mins. Meanwhile, fry the sausages in the remaining oil until they are browned all over, add them to the pan, cover with a lid and cook for 10 mins.

To make the batter, crack the eggs into a bowl or jug, then add the flour and whisk together until smooth. Gradually add the milk and carry on whisking until the mixture is lump-free. Season. Pour the batter into a jug, cover and chill for at least 30 mins and up to 24 hrs.

While the casserole is cooking, or when you’re ready to serve your Sunday lunch, heat oven to 230C/210C fan/gas 8. Drizzle a little rapeseed oil into a 30cm frying pan with an ovenproof handle and put it in the oven for 5 mins. Pour the batter into the pan, put it back in the oven and cook for 25 mins. Check the Yorkshire pudding. It should have a good dark brown colour at the edges and feel firm and dry. If it’s ready, take it out and keep warm. To serve, spoon the sausage casserole into the Yorkshire, and scatter over the parsley, if you like.