To make the curry paste, place the onion, garlic, turmeric, garam masala, coriander, cinnamon, cumin, paprika, cardamom, nutmeg and chilli flakes, if using, in a food processor. Add 1⁄4 cup (60ml) water and process until a smooth paste forms.
Heat the oil in a medium frying pan over high heat. Add the curry paste and cook, stirring, for 1-2 mins or until aromatic. Transfer to a slow cooker.
Add the chicken, tomato, coconut milk, yoghurt, ginger and almond meal to the slow cooker. Cover and cook for 3-4 hours on high (or 5-6 hours on low) or until the chicken is falling off the bone. Season.
Sprinkle with the flaked almonds and coriander sprigs.