Melt the butter with the oil in a large
heavy-based pan. Add the onions and
fry with the lid on for 10 mins until soft.
Sprinkle in the sugar and cook for 20 mins
more, stirring frequently, until caramelised.
The onions should be really golden, full of
flavour and soft when pinched between
your fingers. Take care towards the end
to ensure that they don’t burn.
Add the garlic for the final few mins of
the onions’ cooking time, then sprinkle
in the flour and stir well. Increase the
heat and keep stirring as you gradually
add the wine, followed by the hot stock.
Cover and simmer for 15-20 mins.
To serve, turn on the grill, and toast
the bread. Ladle the soup into heatproof
bowls. Put a slice or two of toast on top
of the bowls of soup, and pile on the
cheese. Grill until melted. Alternatively,
you can complete the toasts under the
grill, then serve them on top.