Cook the potato in a large saucepan of boiling water for 10-15 minutes or until tender. Drain and mash. Add the sour cream and stir until well combined. Season.
Meanwhile, heat the oil in a large, ovenproof frying pan over medium-high heat. Add half the beef and cook for 2 minutes, turning, or until browned. Transfer to a heatproof bowl. Repeat with the remaining beef.
Add the carrot, onion and capsicum to the pan. Cook, stirring, for 5 minutes or until vegetables soften. Add the garlic and paprika. Cook, stirring, for 30 seconds or until aromatic. Stir in the tomato, stock and tomato paste. Bring to the boil. Reduce heat to low and cook, stirring occasionally, for 5 minutes or until reduced slightly.
Add the beef to the vegie mix and cook, stirring, for 2-3 minutes or until heated through. Season.
Preheat an oven grill on high. Top the goulash with the mash, leaving the surface rough. Grill for 10 minutes or until golden. Season with freshly ground black pepper, to serve.
