Toast the coriander and cumin seeds in a medium skillet over medium-high heat until they start to crackle, about 3 minutes.
Use a spice grinder, or a coffee bean grinder, and grind the toasted seeds.
In a large bowl, stir together the ground seeds, turmeric, 1/2 teaspoon salt and pepper (each), cayenne pepper, curry powder, and oil and mix well to form a paste.
Add the chicken to the bowl and stir to coat evenly.
Cover and refrigerate for at least 1 hour, or overnight.
In a saute pan, over high heat, melt the butter.
Add the onion and saute until soft, about 4 minutes.
Add the garlic, ginger, jalapeño peppers, bay leaves and star anise and continue to saute until the onion is lightly golden, about 5 - 7 minutes.
Add the chicken and cook until opaque, about 5 minutes
Add the tomatoes and cook, stirring occasionally, until they soften, about 2 minutes.
Stir in the coconut milk and 1/2 teaspoon salt and bring to a gentle boil.
Reduce the heat to low, simmer until the chicken is very tender, about 20 minutes.
Stir in the lemon juice and simmer for 5 minutes longer.
Remove the star anise and bay leaves, and discard.
Transfer to serving bowl, and top with cashews and cilantro.
Serve with basmati rice (recipe below)