Step 1

Melt the butter in a large, heavy-based saucepan that has a lid, then add the onions and bouquet garni with a generous amount of salt. Stir to coat the onions in the butter, then put the lid on and cook over a medium heat for 45 minutes to 1 hour, stirring every 5-10 minutes to make sure the onions don’t catch.

Step 2

After this time they should be reduced in volume, very soft and a pale golden brown colour. Once they get to this stage, remove the lid 
and discard the bouquet garni. Add the garlic and cook, stirring, over a medium-high heat for a few minutes until the garlic aroma softens, then add the sugar and cook for another 10-15 minutes until the onions are a rich golden colour and taste caramelised. You need to get them right here, as once you add the wine they won’t caramelise any further. Heat the oven to 200°C/180°C fan/gas 6.

Step 3

When the onions are well browned and caramelised, turn the heat up high and pour in the 250ml wine and 50ml brandy/cognac. Bubble briskly for 3-4 minutes to reduce the liquid, then pour in the stock and bring the soup to a gentle simmer. Cook for 10 minutes, skimming off any foam that forms on the surface, then season.

Step 4

Meanwhile, put the baguette slices in the oven and bake for 8-10 minutes until almost completely crisp, but not too coloured. Remove and set aside, then turn the grill to its highest setting.

Step 5

At the end of the simmering time, add the extra glug of wine and splash of brandy/cognac and taste again, seasoning if needed. Ladle the soup into heatproof bowls and top each with 2 baguette slices. Scatter over some cheese and a few thyme leaves, then put the bowls under the grill to melt the cheese.(If you don’t have heatproof bowls, transfer the soup to a large heatproof dish or pan, top with all the baguette slices and scatter over the cheese and thyme, then put the whole thing under the grill.) Serve immediately.