6 large white onions, thinly sliced
sprig rosemary
Dijon mustard
3 bay leaves
2 litres/3½ pints pint good rich beef stock
salt and freshly ground black pepper
1½ tbsp caster sugar
1 tbsp olive oil
50g/1¾oz butter
25g/1oz gruyère cheese, grated
½ thin baguette
200ml/7fl oz white wine