Preheat oven to 200C. Parboil potatoes until tender, 10-12 mins, then drain. Transfer potatoes to a baking tray, drizzle with olive oil, a pinch of salt and pepper, and paprika. Roast for 25 minutes or until golden and crispy.
Chop up onion, garlic and ginger and add to a pot and cook on medium until soft, around 8-10 minutes. Add tomato paste, garam masala, cumin, turmeric, coriander, cayenne and cardamom and cook until tomato paste darkens, around 5 minutes. Add tinned tomatoes and stir to combine. Add chicken stock - adjust amount depending on how thick you want your sauce to be. Reduce heat to low until ready to plate.
Heat 1 tbsp of olive oil in an ovenproof pan over very high heat. Season chicken breasts with salt, pepper, coriander and paprika and make sure chicken is evenly coated. When pan is smoking, place chicken in and leave untouched for 1.5 minutes, then flip and cook for 1.5 mins on the other side. When 3 minutes is up, place pan in oven for 9 minutes. The potatoes should nearly be finished - cover either potatoes/chicken until the other has finished cooking.
When potatoes are cooked, remove from oven and press down firmly with a potato masher to crush. Serve chicken on top of potatoes with curry sauce.