How to make Mallika Basu's ultimate simple chicken curry

Name: How to make Mallika Basu's ultimate simple chicken curry
Cuisine: Asian, Indian
Ingredients: 1 large onion, peeled and sliced; 4 garlic cloves, peeled and chopped; Half inch ginger, peeled and chopped; 3 tbsp oil; Pinch of granulated sugar; 2 medium tomatoes, chopped; 1 tsp chilli powder; Half tsp turmeric powder; 2 tbsp Greek-style natural yoghurt; 4 large chicken thighs and drumsticks, skinned; 1 tsp garam masala; Salt to taste; Chopped fresh coriander, to garnish