Step 1

Heat oven to 200C/180C fan/gas Put the onions in a roasting tin with the oil, salt and pepper. Give it a good stir, then roast for 45 mins, stirring halfway through, until the onions are tinged brown, but not burnt.

Step 2

Tip the onions into a large pan with the stock, mustard and Marmite. Bring to the boil and simmer for 15 mins, then stir in the parsley. Toast 4 of the bread slices then scatter on the cheese. Ladle the soup into bowls, pop a toast into each and serve with the extra slices of bread on the side.