French onion soup with cheesy croutons

Serves 4
2hrs 30 mins to cook
Recipe from Nick Haddow's new book Milk. Made, published by Hardie Grant. "There are some dishes that I could never get sick of and this is one of them. I could eat it every day. This soup is an exercise in balance and every time you make it will require a different touch, as onions change in their sweetness and acidity throughout the year." - Nick Haddow