Preheat the oven to 350f / 180c. Get the croutons going before you start with the soup as they will need a bit of time to crisp up in the oven. To make the croutons, heat olive oil and butter in a small saucepan until melted. Take off the heat and stir through the mustard and the sea salt. Toss with the chunks of bread until very well coated and spread out onto a baking tray. Bake in the oven until deeply crispy and golden, mine took about 20 minutes but do keep an eye on them as you want them to come out just before burning point. Remove from oven and keep warm until soup is ready. 

Meanwhile start the soup by heating a large heavy-bottom soup pot over medium heat. Melt the butter and olive oil and stir in the onions, cook until softened and beginning to go translucent. Throw in the potatoes and cook for 5-7 minutes until they are starting to soften. Add the garlic and stir for one minute until fragrant, season with black pepper. Add the vegetable stock and bring to the boil, turn down to a simmer and cook the potatoes until almost done. When the potatoes are almost done are still tender crisp, add the broccoli and cook for a further 5 minutes until the broccoli stalks are soft enough to whizz up, but still vibrantly green. 

Take the pot off of the heat and puree with an immersion blender, I like mine very silky. Once you have pureed to your liking, put the pot back on the stove over the lowest possible heat. Add the stilton to the pot and let it cook through just until the stilton begins to melt and give a gorgeous creamy texture to the soup. Adjust seasoning and serve. 

I love this with heaps of croutons, a few more crumbles of blue cheese and a slight sprinkling of cayenne pepper for a burst of heat. Slurp immediately.