Peel and dice the yam into medium pieces. Place in a large pot with cold water, salt, and bring to a boil.
Boil for about 25–30 minutes until the yam is very soft and easily pierced with a fork. Drain and return to the pot.
Yam Pie is a staple of the Bajan Sunday dinner. Use a good, white or yellow yam. Boil the yam until very soft so it can be mashed into a smooth puree. The addition of evaporated or whole milk and fresh herbs is key to the rich, Caribbean flavor.
Peel and dice the yam into medium pieces. Place in a large pot with cold water, salt, and bring to a boil.
Boil for about 25–30 minutes until the yam is very soft and easily pierced with a fork. Drain and return to the pot.
Preheat the oven to 180 °C (350 °F). Lightly grease a baking dish (approx. 20x25 cm).
Add the butter, milk, onion, garlic, thyme, nutmeg, salt, and pepper to the cooked yam. Use a hand mixer or a fork to mash into a smooth, creamy puree. Add a little more milk if the mixture seems too stiff.
Transfer the yam puree into the prepared baking dish and smooth the top.
Sprinkle the top evenly with grated cheese.
Bake for 20–25 minutes, or until the cheese is golden and the mixture is bubbling underneath. Let cool for 10 minutes before slicing and serving so it holds its shape better.