Preheat the oven to 220 degrees (200 fan) or Gas Mark 7. Select a large baking tray or ovenproof dish about 26 x 20 cm
Thinly slice the sweet potatoes by hand.
Use one-quarter of the sweet potatoes to create an overlapping layer in the base of the baking tray or dish. Distribute one third of the garlic and thyme over the potato layer and season generously with salt and pepper. Repeat the layering process, finishing with a layer of sweet potato slices. Pour over the coconut milk, then gently press down on the contents of the dish with a spatula to compress, season with salt and pepper and sprinkle with the reserved thyme.
Bake for 20 minutes in the pre-heated oven, then press down on the potato slices with the spatula to submerge them in the coconut milk. Return the dish to the oven and bake for a further 20-25 minutes.