Heat a large, heavy-based casserole dish over a moderate heat. Add the sunflower oil, then season and sear the lamb, in batches if necessary, until golden brown in colour all over. Remove from the dish to drain, then add the carrots and potato and saute for 2-3 minutes, stirring occasionally.
Add all the lamb back to the dish and sprinkle the flour on top, stirring well to coat. Add the wine and let it reduce by half. Cover with the stock, then bring to the boil. Add the rosemary sprigs, then reduce to a simmer, cover, and cook gently for 60-70 minutes until the lamb is soft, tender and cooked through. Stir in the frozen peas at this point and allow the dish to come back to a simmer. Remove from heat and adjust the seasoning if necessary.
Spoon into shallow soup bowls. Serve immediately.
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