Heat the oil in a 23cm pan with a lid and sauté the onion, carrot and celery for a couple of minutes until just beginning to soften. Stir in the rosemary with the beef cubes and sauté until golden on all sides.
Add the Marmite, Worcestershire sauce, mustard and flour and cook for 1 minute, stirring. Pour in the stock and bring to a simmer, then cover and simmer gently for about 1 hour or until the beef is tender and the sauce has slightly reduced and thickened, stirring occasionally.
Meanwhile, preheat the oven to 200°C/400°F/Gas Mark 6. To prepare the soufflé topping, place the cream, butter and Cheddar cheese in a small pan and melt over a low heat until runny – don’t worry if the mixture looks a bit curdled, as this is normal. Pour into a large bowl. Whisk the egg white until stiff and then fold into the melted cheese mixture. Season to taste and carefully fold in the bread cubes until evenly coated.
Quickly spoon the soufflé topping on top the braised beef base and transfer to the oven for another 25-30 minutes or until the soufflé topping is golden brown and bubbling. Serve immediately with the buttered peas.