Heat oil + butter in another pot or pan. Add cumin first and let them crackle & get browned.
Then add onions and saute them till they caramelized or golden browned.
Take care not to burn them as this will impart bitter tones in the curry.
Light browning the onions is also alright.
Keep on stirring the onions while sauteing them, for uniform cooking and also so that they don't get burnt.
Add the ginger-garlic-chili paste. Stir and saute for 5-10 seconds on a low flame.
Add the tomatoes. Saute for 2 to 3 minutes till the tomatoes become soft.
Add all the spice powders one by one - turmeric powder, red chili powder, coriander powder, asafoetida (hing) and garam masala powder.
Stir and saute the whole masala mixture till the fat starts leaving the masala.
Use a slotted spoon or a strainer and remove the beans and add them to the masala.
You can also strain the rajma first and keep it aside.
Keep the stock also aside. Stir and saute for a minute.