You can make this masala on stove top as well as microwave. I will demonstrate the microwave method.
500 gms onions chopped finely in a food processor
1 slightly heaped tsp ginger garlic paste
1 Tbsp oil ( you can reduce it slightly)
1/2 tsp cumin seeds
6 tomatoes chopped coarsely in a food processor
1 tsp chilli powder
1 tsp coriander powder
1/2 tsp turmeric powder
I prefer adding garam masala and salt at the time of making the dish.
Take a large microwave bowl.
Put the chopped onions and 1 Tbsp oil and cuminseeds.
Microwave on HIGH for 3 minutes.
Then microwave on 600W for 10 minutes.Stir and again keep for another 10 minutes.
Still cooking at 600 w reduce the time intervals now to 5 minutes and then to to 3 minutes. Stirring in between .
During the last stage be careful the onions might burn. Stop when onions are golden in colour.
The total time required would be around 35 minutes at 600w. If you cook at HIGH the time required will definitely reduce.
Someone guided me not to do prolong cooking at HIGH, so I cook at 600W.
Now add the ginger garlic paste and mix. Micro again at 600W for 10 seconds.
Add the tomato puree , chilli powder,and turmeric powder to the masala. Mix well.
Now Micro at HIGH for 3 minutes.
Reduce to 600 W and micro for 7 minutes. Stir and micro again for 5 more minutes.
Now reduce the time intervals to 3 minutes.
Micro till the whole masala is deep maroon red and not pulpy. It should be dry paste and can form a lump. Most of the water is eliminated.
So this can safely be kept in the fridge for 8 days.
These ingredients should make approx.1 cup of masala.