Heat the butter in a large pan over a low heat. Add the chopped onion and cook gently for about 10 minutes until the onion is soft.
Add the ginger, garlic, curry powder, Chinese five spice and turmeric. Cook for a couple of minutes, stirring often.
Add the coconut milk, water, soy sauce and sugar and crumble in the stock cube. Bring up to a gentle simmer and cook for 10 minutes.
Transfer the sauce to a blender and blitz until it is smooth then return it to the pan.
Place the cornflour in a small bowl and stir in 2 Tbsp cold water to form a slurry. Stir the slurry into the sauce then bring it up to a simmer. Cook for a couple of minutes, stirring constantly, until the sauce has thickened.
Season the sauce to taste with salt and pepper then serve with your choice of stir fried vegetables and/or cooked vegan chicken pieces or baked tofu.