In a heavy bottom saucepan add oil and butter, once hot add in the thinly sliced onions, sugar and cook on a low fire for approximately 30 mins until well caramelised and soft
Once the onions are caramelised and turned slightly golden brown colour.
Deglaze with white wine and scrape all the caramelised parts that are stuck on the bottom of the pan. Let it absorb all the alcohol for 1 minute,then add flour and cook for further 1 minute
Then add the stock, Prepared Bouquet Garni and cook on a low fire for 20-30 mins, checking occasionally
After 20-30 mins check to season, take the soup off the fire. Take out the bouquet garni and discard