Start by making the sweet potato chips. Scrub the potatoes but don't peel, then cut them into finger size chips lengthways, about 1-2 centimeters. Drizzle with a little olive oil and sea salt and place in the oven whilst you make the curry sauce.
In a heavy base pan, heat the coconut oil. Once melted and hot add in the curry leaves. Quickly followed by both the seeds. The mustard seeds should start pops straight away. Turn the heat down immediately. Add in the garlic and chilli. Let this cook down for for several minutes. Add the spices to coat and give the mix a stir. Add in the coconut milk and turn the heat backup. Let this cook down for about 12 minutes until all the flavours have infused and the sauce has thicken slightly.
Check on the chips ever so often, giving them a toss to make sure they don't catch and are evenly cooking. This should take about 20 minutes or so. Push the sauce through a sieve if you want it really smooth, and serve on the side of the chips.
