Method

• 1.
  Melt butter and oil in a large heavy-based pot (5.5L-capacity) over medium heat. Fry onion and eschalot for at least 1 hour or until softened, stirring only every 15 minutes to begin with.
• 2.
  Increase heat to medium-high and cook, stirring constantly, for 20-25 minutes until dark brown. As you feel the onions catch on the base of the pan, add half the wine and watch it sizzle as the alcohol burns off. Add remaining wine and scrape pot with a wooden spoon. When the liquid is almost gone, reduce heat to medium.
• 3.
  Add stock in four batches, stirring occasionally, cooking for 3 minutes after each addition. Finally, add thyme and simmer for 20 minutes. Season to taste. It will need a fair amount of salt, as the onions make it naturally sweet.
• 4.
  While soup is simmering, cut your baguette into 6cm lengths, splitting each in half lengthways. Rub cut side with garlic. Heat oven grill to high. Grill bread, cut-side down, for 3 minutes or until golden. Flip and grill for 1 minute or until pale golden.
• 5.
  Combine port and egg yolk and beat to combine, then stir through the soup (this is a trick that Lyon cooks use to give the soup some creaminess. You can also use a spoonful of Dijon mustard stirred into some cognac.) Discard thyme sprigs.
• 6.
  Pour soup into ovenproof bowls and top with baguette pieces, cut-side up. Top each piece of baguette with cheese and place bowls under grill for 3-4 minutes to melt. Sprinkle with extra thyme and serve with a warning that the bowls are very hot.