Caramelised onion and Cantal soup | Gourmet Traveller

Ingredients

• 60 gm butter, coarsely chopped
• 2 tbsp olive oil
• 4 onions, thinly sliced
• 2 tbsp thyme leaves
• 2 garlic cloves, finely chopped
• 1.5 litres (6 cups) vegetable stock
• 6 slices day-old rye bread
• 200 gm Cantal (see note), coarsely grated, plus extra to serve