In a blender or grinder, add the onions, cashews, black peppercorns, fennel, chiles, and a few tablespoons of water. Pulse until smooth paste forms, adding additional water just until it is smooth but not runny.
In a skillet, heat oil over medium heat and add in the ptoatoes. Saute them for 5 to 6 minutes, until they are fork-tender. Remove from the pan and set aside.
In the same pan, add the cumin seeds, cinnamon stick, green cardamom, star anise, cloves, and mace. Stir cooking them for 1 minute.
To the skillet add the turmeric and red pepper flakes and saute for another 1 minute.
Then add in the cashew paste and saute, stirring regularly, for 2 minutes.
Add 2 cups of water to the skillet, and then let it simmer for 3 minutes.
Add in the potatoes and salt to taste. Simmer until desired consistency. Serve with rice, chapati, or naan as desired.