Recipe: steak with red wine sauce

OK, this is not a frugal recipe, not with steak.  However, the sauce was lovely and I reckon it would be good with meatballs or a burger without a bun too. 
Anyway, sometimes frugallers want a treat and this was a real treat!

Ingredients for one
the steak (or whatever)
oil, salt, pepper
some onion, finely chopped (could also use mushroom, pepper, etc)
bit of red wine (I got one of those mini bottles and drank the rest!)
bit of balsamic vinegar
about 1/4 stock cube (if you're making enough for one, more for more)
good pinch of mustard powder
a tsp redcurrant jelly (I bet you could use something like marmalade instead)
I also used a few thickening granules but that's not necessarily needed, it depends how runny you want it.

Method.
Cook the steak the usual way by heating up the pan, oiling and seasoning the steak on both sides and when the pan is really hot, cooking for four minutes on each side or until it is how you like it.  Pop the steak on a plate and keep it warm.

Reduce the heat under the pan.  There may be enough fat from the meat but if not, add a little more oil.  Fry the onion until it's soft and golden. stirring well so that all the meaty bits get mixed in.  Then add the wine, the balsamic vinegar, the stock cube and the mustard and stir well until it boils.  Then add the jelly and stir while it blends in.    Let it reduce down a bit and add the granules if you want it thicker.  Taste and season as needed.

Then you can either pop the steak back in the pan so the sauce covers it all over, or you can put the sauce in a jug and pour it over the steak at the table.
Either way it is lovely!

Now I am wondering if one could use red wine vinegar instead of the real deal.  I'll just have to try it and see, maybe with a burger or something.