1) Heat the oil in a large saucepan and then add the onions. Cook on a medium heat until soft. 2) Add the celery, leek, potato and butter. Stir until melted, then cover with a lid. Allow to sweat for 5 minutes. 3) Remove the lid. Pour in the stock and add any chunky bits of broccoli stalk. Cook for 10 – 15 minutes until all the vegetables are soft. 4) Add the rest of the broccoli and cook for a further 5 minutes. 5) Transfer to a blender and blitz until smooth. 6) Stir in the stilton and allow to melt. Re heat if needed. 7) Season with black pepper and top with toasted croutons (optional) serve.