Slow Cooker Lamb Rogan Josh

• 1.5 lb (680g) lamb neck filet
• 1 white onion, sliced
• 2 tbsp. olive oil

For the paste:

• 3 tbsp. tomato paste
• 3 garlic cloves, minced
• 1½ tsp. cumin
• 1½ tsp. garam masala
• 1 tsp. ground ginger
• ½ tsp. ground black pepper
• 2 tsp. paprika
• 1 tsp. smoked paprika
• 1 tsp. chili powder
• 1 tsp. salt
• 1 beef stock cube, crumbled
• 1 tbsp. olive oil 

For the sauce:

• 1 cup (250g) natural yogurt
• 1 tbsp. cilantro, chopped
• ½ tsp. coconut sugar
• 1 red chili, seeds removed, finely chopped
• 14 oz. (400g) tomato sauce
• ¼ cup (60ml) water
• 2 bay leaves
• 1 tbsp. cardamom pods
• 1 cinnamon stick