01 - Preheat oven to 375°F (190°C). Lightly grease a 2-quart baking dish.
02 - Add yam cubes to a large pot, cover with water, and incorporate salt. Bring to a boil, reduce heat, and simmer for approximately 15 minutes until just tender. Drain thoroughly.
03 - Using a potato masher, mash drained yams in a large mixing bowl until mostly smooth. Blend in melted butter, packed brown sugar, ground cinnamon, ground nutmeg, heavy cream, and vanilla extract until fully combined.
04 - Evenly spread the yam mixture in the prepared baking dish.
05 - Distribute pecan halves or pieces over the yam layer, then cover with mini marshmallows.
06 - Bake uncovered for 20 to 25 minutes, or until marshmallows are golden brown and dish is heated through.
07 - Allow to cool briefly before serving.