Potato & Spinach Vindaloo

For the curry paste

• 4 cardamom pods
• 2 tsp coriander seeds
• 1 tsp mustard seeds
• 1 tsp fennel seeds
• 2 cloves
• 3 tsp ground cumin
• 1 tsp ground cinnamon
• 2 tsp hot curry powder (use 1 tsp if you prefer a milder curry)
• 2 medium red chillies, seeded and finely chopped
• 1 tsp fine sea salt
• 2 tbsp tomato paste (concentrated purée)
• 40ml white wine vinegar
• 30ml vegetable oil

For the rest of the dish

• 2 tbsp vegetable oil
• 2 onions, chopped
• 175g tin chopped tomatoes
• 1 tbsp caster sugar
• 1 tsp fine sea salt
• 650g boiling potatoes, peeled and chopped into 3 cm dice
• 100g English spinach or Swiss chard
• Chopped coriander to serve