Arvi Ka Salan Colocasia Taro Root Curry

Name: Arvi Ka Salan ( Colocasia / Taro Root Curry )
Ingredients: 500 gm. Colocasia / Taro Root ( Arvi ); 1/4 cup oil; or less; 125 gm. ( 2 medium ) onions, thinly sliced; 250 gm. tomatoes, chopped; 1 tsp. cumin seeds; 1 tbsp. ginger garlic paste; 6 - 8 whole black pepper; 4 - 5 cloves; 2 large cardamom; 2 inch piece cinnamon stick; 1 tbsp. coriander powder; 1 tbsp. red chillies powder; 1/4 tsp. turmeric powder; 1 tbsp. salt, or according to taste; 1/2 tsp. garam masala powder; 2 -3 green chillies; 2 tbsp. fresh coriander leaves, chopped