Preheat the oven to Gas Mark 4, 180°C, fan 150°C. Start by peeling the red peppers, then half them lengthways and remove the seeds. Arrange in a roasting dish with the cut-sides facing down. Drizzle the peppers with 1 tablespoon of olive oil and season with salt and pepper. Place in the oven for around 10 minutes until the peppers have softened. Take out and leave to cool, then slice into 1cm strips. Set aside. Mix 1 pinch of salt with the plain flour and get the kids to use their hands to cover the diced beef in a light coating of the flour. Set a large flameproof casserole dish over a high heat and add the butter and the rest of the oil. Once the butter has melted, add the coated beef a portion at a time until brown all over. Remove each batch with a slotted spoon before moving on to the next batch. Once all the beef is ready, add the onions to the pan and cook for 4-5 minutes until golden brown. Add the smoked paprika and pepper strips. Cook for 1 minute before pouring in the beef stock. Return the browned beef to the casserole dish, stir and cover. Place in the oven and cook for 1.5 hours until the meat is tender. Take the stew out of the oven, season to your liking then skim off any fat from the surface. If you're preparing this in advance, the dish can now be left to cool and stored in the refrigerator for 2-3 days. When reheating ensure that the dish is piping hot before serving. Meanwhile, prepare the spaghetti by boiling in salted water for 8-10 minutes until al dente. When ready to serve, add spaghetti to each bowl, mix the sour cream into the goulash and place over the spaghetti. Sprinkle the chopped chives over the top and serve immediately.