Heat butter in a pan. Add in cumin seeds, whole cloves, green cardamom, whole pepper corn and cinnamon stick. Saute until cumin seeds start to fragrant and turn deeper in color.
Then add in sliced onion, ginger, garlic and serrano with ½ tsp of salt and cashews. Mix well and cook until onions are completely translucent and just starting to turn brown.
Once done, turn the heat off and let it cook down a little. Then add onion mix to high speed blender with ½ tsp of salt, ½ tsp of garam masala and 1½ cup of milk. Blend until completely smooth. Then add in ½ cup of heavy cream and do few pulses so that it mixes well with the sauce.
Peel and slice potatoes in ⅛ inch thickness and coat them all with ¼ tsp salt, ½ tsp black pepper powder, ½ tsp garam masala and ⅛ tsp of ground nutmeg.
Layer ⅓ of the potato slices in a greased baking tray. Then pour ⅓ of the sauce. Continue to layer rest of the potatoes and sauce in 2 other layers.
Once all the potatoes slices and sauce are well arranged in the baking tray, bake it uncovered on 375℉ for 50 minutes.
After 50 minutes of baking, take the tray out and top it with freshly shredded yellow and white cheddar cheese then bake it uncovered for another 15 minutes or until the cheese it well melted and bubbly.
Sprinkle with chopped scallions and cilantro and enjoy!