1.Trim all visible fat from beef; cut into cubes.
2.Toss beef in flour. Shake off any excess flour.
3.In a large saucepan, heat oil on medium heat, cook beef for about 2-4 minutes, or until browned all over. Remove from pan.
4.Add leek, pepper and mushrooms to same pan; cook for about 5 minutes, or until leek is soft.
5.Add beef, tomato, beer, water and paste to pan; bring to a boil. Simmer, covered, for 40 minutes; remove lid.
6.Simmer for a further 10 minutes, or until sauce has thickened slightly and meat is tender.
7.Transfer to a casserole dish and top with herbs. Serve.
Casserole can be made a day ahead; cover, refrigerate until required.Note