1. If possible, cook meat in the pan first
  2. Carmelize/brown your onions in a pan
  3. Once they're good and soft, add about 2 tbsp (not precise) of balsamic vinegar to deglaze the pan (scrape it up gently with a fork)
  4. Sprinkle a heaping tbsp of plain flour on top.
    1. The onions will get a nice balsamic paste attached to them
  5. Heat for a minute or so to get a pseudo-roux
  6. Add 500ml of beef stock
  7. Put on high heat until thickened (about 5 mins)