Potato, Onion and tomato dry curry (Vengayam, thakkali and urullai masal)

Potato, Onion and tomato dry curry (Vengayam, thakkali and urullai masal) - Preparation time 15 mins
I thought of making potato curry slightly different from my usual potato curry. This tasted different and with sour, spicy taste. Potato curry went well with sambhar rice. I tried in small quantity.

Ingredients:-
Potato - 1 (big size) pressure cooked and peeled of the skin
Tomato - 1 (medium size) chop to small pieces
Onion - 1 (chopped to thin slice)
Sambhar powder - 3/4 tsp
Turmeric - 1/4 tsp
Sesame oil - 1 tbsp
Salt - to taste
Mustard - 1 tsp
Urad dhal - 1 tsp
Fresh coriander - 2 tbsp

Preparation method:-
Heat the oil in a kadai. Add mustard seed to splutter, urad dhal to become golden brown.
Add the onion and fry till it get cooked and add chopped tomato. Fry for few minutes till both onion and tomato become soft and oil starts leaving. Add sambhar powder, turmeric powder
along with salt. Cook till raw smell goes off.
Now add the cooked potato cubes, coriander leaves to the fried items.
Turn the potato cubes well for 5 to 10 mins in low flame, so that all the fried ingredients gets coated well.