Mustard Beef Stroganoff

I tried to take a photo of this but no matter how I tried I couldn't make it look pretty and attractive, and we were hungry and the other half though I was a bit weird

500g beef rump, cut into strips
2 medium onions, sliced
oil spray
250g sliced button mushrooms if you like them, we don't - blurk fungis!
3 Tbs wholegrain mustard
150g sour cream (I use low fat)
1/2 cup beef stock
1/2 cup white wine
salt and freshly ground black pepper

Brown the beef in the oil in a hot non stick frypan, just seal and brown don't cook  through as that will happen later.  Remove from the pan.  Saute onions in the pan until caramelised a golden brown.  Add the mushrooms if using - yuck!  Season with freshly ground black pepper.,  Add the wine and stock and simmer until reduced a bit (not long, maybe 5 mins).  Lower heat and add the beef and any meat juices back to the pan and stir in mustard and sour cream.  Simmer until the sauce has reduced a bit and beef is cooked through (another 5 mins - ish).  Serve over rice, noodles or our favourite, mashed potatoes.