Coat meat in seasoned flour and brown in oil in batches for 4 minutes.
Deglaze the pan with wine and pour over the meat in a saucepan.
Sauté chopped onion until soft and add to the meat.
Fry mushrooms briefly, then add to the saucepan with bay leaf, sauce, stock, and seasoning.
Simmer covered with dampened greaseproof paper for 90 minutes until tender and let cool.
Mix crust ingredients with enough water to form a soft dough.
Roll out most of the dough to 5mm thickness and line a greased 1.2 litre basin.
Spoon the meat filling and some gravy into the basin.
Cover with a dough lid, pinch edges to seal, and trim.
Tie a greased foil or paper cover loosely over the basin with string.
Steam the pudding in a covered pot of simmering water for 90 minutes.
Fry sliced onions until golden, add wine and stock, reduce by half, and stir in mustard.
Serve pudding wedges with the hot onion gravy.