Heat the oil in a large pan over medium heat. Add the onion and cook for a few minutes until they turn translucent.
Add the garlic, ginger, and green chillies. Sauté for another 2-3 minutes until fragrant.
Stir in the garam masala, cumin, and ground coriander.
Add the chopped tomatoes, tomato paste (puree), sugar, veg stock, and Brussels sprouts. Cook for 5-7 minutes, until the tomatoes break down, the mixture thickens, and the sprouts and tender.
Stir in the yoghurt and add salt to taste.
Serve the curry with rice or Indian bread like naan or roti. Top with fresh cilantro (coriander) if using.