Peel and slice potatoes into 1-inch cubes. Boil until just cooked through but still firm. Drain and set aside.
Heat the olive oil in a large skillet over medium-high heat. Fry the onion and garlic until starting to color and fragrant, 3-5 minutes. Stir in the spices, salt and pepper and coat the onion mixture completely. Fry for another 2 minutes so the aromas of the spices start to come out. Add the coconut milk and stock (or water) to the pan. Carefully tip in the cooked potatoes and stir gently. You do not want the potatoes to break up. Once everything is coated in the curry sauce, turn the heat to low and gently simmer for 10 minutes. At the end of cooking, stir in the lime juice and the spinach. The spinach will wilt into the sauce.
If you find the curry is not liquid enough, simply add in some more vegetable stock or water. Enjoy with some fresh naan bread.