In a wide heavy bottom pan, melt in 4 tbsp of salted butter. Once melted add in cumin seeds, cloves, peppercorn, cinnamon stick, black & green cardamom, bay leaf and whole dry red chilis.
Cook whole dry spices in butter for 20-23 second on medium heat or until the cumin seeds start to fragrant and change into deeper brown color.
Add chopped onions with 1 tsp of salt. Mix well and cook for about a minute on medium heat.
Add in ginger, garlic, serrano. Mix well and cook on medium heat until raw smell of garlic is gone and onions are translucent. Do not burn them.
Add in chopped tomatoes and tomato past. Mix well.
Add in all the other spices listed under gravy (tandoori masala, garam masala, cumin coriander powder, turmeric powder, kashmiri red chili powder and 1 tsp of salt). Mix well.
Add in 1 cup of water as the tomato paste makes this spice mix clumpy and some what dry. Mix well, cover and cook until the added water starts to evaporate and butter starts to separate. Uncover and mix few times during this step.
Once the spice mix is ready, remove the bay leaf. Take it out in a high speed blender. Once it cools down a little, blend it smooth. Once done, keep aside.