Brush the beef with mustard and season with salt, pepper, and paprika powder.
Cut a large piece of roasting parchment. Cut the onion into 8 pieces and halve the stock cube. Place the seasoned beef in the center of the parchment, arrange the onion pieces and stock cube halves on each side of the meat, pour the water around the meat, then tightly seal the parchment on all sides. Pierce the top 10-15 times with a pin.
Preheat the oven to 200°C (392°F) with top and bottom heat (not fan setting). Place the sealed parchment on a baking sheet and cook for 100 minutes.
Carefully open the parchment and transfer the beef to a serving platter. Pour the cooking liquid into a saucepan, puree the cooked onions and mix back in. Add the cremefine and red wine, bring to a boil for 1-2 minutes, then thicken with dark sauce thickener to your desired consistency.