Instructions:
- Remove sausage casings (if present) and brown the meat thoroughly in a large skillet over medium-high heat. Drain excess fat and set the sausage meat aside.
- Melt butter in the same skillet. Add leeks and carrots; cook gently until softened, about 8–10 minutes. Add garlic and cook for 1 minute more until fragrant.
- Stir in the flour (if using) and tomato purée; cook for 1 minute. Deglaze the pan with wine/cider, scraping up any browned bits (fond). Allow to bubble and reduce slightly.
- Pour in the stock, add thyme and Worcestershire sauce. Bring to a gentle simmer. Cook until the sauce has thickened slightly (about 5–7 minutes). Season generously with salt and pepper.
- Stir the cooked sausage meat and frozen peas back into the vegetable mixture. Pour the entire mixture evenly into a prepared oven-safe casserole dish (approx. 3-quart capacity).
- In a bowl, whisk together the eggs and milk/cream until smooth. Stir in the grated cheese and chives. Season lightly with salt and pepper.
- Gently pour the egg mixture evenly over the sausage filling in the casserole dish, ensuring it flows into all the gaps.
- Bake in a preheated oven at 375°F (190°C / Gas Mark 5) for 35–45 minutes, or until the custard topping is set, puffed, and beautifully golden brown.
- Let the casserole rest for 10 minutes before slicing and serving. Serve hot with mashed potatoes and green vegetables.