I first cooked this from a Delia Smith receipe. I adapted it and tweaked it for my own take on it

It always goes down well and is the one everybody asks for !

Compared to a lot of other soups, this one can be quite time consuming if you want to get it right.
For this reason I suggest you cook a decent batch as it can always be frozen.

This will serve around 8-10

Ingredients:

Cooking onions
Rather than give you a weight of unpeeled onions I am going to suggest you peel enough
so you end up with about 1.8 – 2.0 Kg after skinning.
Around 3 cloves of garlic (crushed or finely chopped).
6 or 7 Shallots.
2 big tablespoon scoops of butter.
1 1/2 Tablespoons of olive oil.
Beef Stock cubes to make 2 litres of Stock. (Good old Oxo works best)
Large glass of white wine.
1 heaped tablespoon of demerara or brown sugar
Salt + Black Pepper

For Serving:
Some crusty bread/sliced baguette
Gruyere cheese, grated.

Method
Slice/chop the onions and shallots. I try and mix some sliced and some chopped..(trust me it works)

Melt the butter and olive oil in the largest pan you’ve got. A heavy bottomed pan works best.
Add the onions and shallots and crushed garlic.
Cook on a medium heat, stirring for around 5 minutes.
Add the sugar and stir in.
Cover and lower the heat.

This is where the time and patience comes in.
The onions need to do two things. We need to sweat them down and then caramelise them in combination with the sugar.
Keep checking the onions as they sweat down, striring occasionally.
When the onions are nice and soft, remove the lid and turn up the heat a little.
The plan is to now reduce the liquid by simmering and get the onions to caramelise on the bottom of the pan.
You will have to monitor the progress, stirring every now and then as the liquid evapourates.
Quite suddenly the onions will start to stick to the bottom of the pan and turn a golden brown colour.
As this happens you need to turn them regularly with wooden spoon to get them just up to the point before they burn.

When most of the liquid has gone and the onions are caramalised nicely, add the white wine.
Simmer uncovered for about 4 minutes then start to add the stock, stirring in slowly.
Cover and simmer on a very low heat for around 40 mins, just remember to stir a couple of times to make sure the onions are not sticking to the bottom of the pan. Turn up the heat for the last 10 minutes and simmer uncovered.
Add salt and pepper to taste.

Put on the grill. Put grated Gruyere cheese onto slices of baguette and pop under the grill until the cheese has only just melted.

Ladle the soup into bowls and drop in a slice of the Gruyere baguette, cheese side up, then place the bowl back under the grill until the cheese bubbles.

Serve straight away piping hot.

Remember to tell your guests that the bowls will be hot.

Enjoy.