Slice the mushrooms, chop the onion and parsley, dice the red bell pepper, and cut the beef into small cubes or thin strips.
Heat sunflower oil in a large braiser or deep skillet over medium heat. Add the beef and sauté for 3–4 minutes until lightly browned.
Add the chopped onion, season with sea salt and black pepper, and sauté for about 1 minute. Stir in the bell pepper.
Pour in 50 ml of water, cover, and let it simmer for 5 minutes over medium heat.
Add Hungarian sweet paprika and dried marjoram, then stir in the sliced mushrooms. Cook for 3 minutes.
Pour in about 700 ml warm water, season lightly with salt, cover, and simmer for 5–7 minutes until mushrooms are tender.
Dissolve the cornflour in cold water to create a smooth paste.
Stir the cornflour mixture into the pot, add double cream and vegetable soup mix, and simmer for 2–3 minutes until thickened.
Remove from heat and stir in freshly chopped parsley.
This Hungarian Mushroom Paprikash is best served warm over penne pasta, rice, polenta, or fresh crusty bread.