Heat 1 tbs oil in a large frying pan over medium-high heat. Cook the beef, in batches, turning, for 8 minutes or until browned. Transfer to a heatproof bowl.
Heat remaining oil in pan. Cook the mushroom and shallot, stirring, for 5 minutes or until golden. Add to beef. Cook speck and garlic, stirring, for 3 minutes.
Stir in beef mixture. Add Guinness, stock, tomato paste, thyme and bay leaves. Bring to the boil. Cook, partially covered, for 2 hours or until beef is tender. Season.
Meanwhile, to make the colcannon mash, cook the potato in a saucepan of boiling water for 15 minutes or until tender. Drain well and return to pan. Use a potato masher to mash the potato until smooth.
Heat butter in a large frying pan over medium heat until foaming. Add the cabbage and shallot and cook, stirring, for 3-4 minutes or until tender (do not brown). Add to potato and stir to combine. Season.
Preheat oven to 180C/160C fan forced. Spoon beef mixture into a 3L (12 cup) ovenproof dish. Top with mash. Rough with a fork. Cover with cheese. Bake for 30 minutes or until golden. Sprinkle with extra thyme.
