Heat oil in a large skillet over medium high heat. Add onion and garlic, cook for 1 minute. Then add carrots, celery, thyme and rosemary. Cook for 3 minutes or until softened and sweet.
Turn heat up to high. Add lamb and cook, breaking it up as you go, until browned.
Add flour and mix in. Add tomato paste, broth, red wine, bouillon cube, Worcestershire sauce and bay leaves. Stir well.
Bring to simmer, then turn down heat so it is simmering rapidly - I have it on medium. Cook for 30 minutes, stirring occasionally, until it reduces down to a thick gravy consistency (Note 1) (see video).
Adjust salt and pepper to taste. Transfer Filling to 1.5 litre / quart pie baking dish. Stir through peas. Cover, then refrigerate to cool for 1 - 2 hours or overnight (optional, Note 2)