Preheat oven to 350℉. Butter an 8x8 baking dish (this recipe would easily double into a 9x13 pan).
Cut sweet potatoes into halves or thirds and place in a large pot.
Cover potatoes with water and bring to a boil. Simmer until potatoes are very tender when pierced with a fork or knife, about 25 minutes.
While potatoes cook, make the candied pecans. In a small skillet melt the butter. Once melted, add the brown sugar and stir to incorporate. Once incorporated, add the pecans. Stirring occasionally, cook until the pecans are nice and fragrant. Just before removing from the heat, sprinkle with a little salt. Pour onto wax or parchment paper to let them cool and harden. Once cooled, roughly chop them.
Drain potatoes. Cool enough to handle, then rub skins off with your hands.
While potatoes cool, melt the butter in a medium sized glass bowl. Whisk in the brown sugar, ginger, coriander, cinnamon, and salt. Then, add the coconut milk and whisk until all combined.
Once the potatoes are peeled, return them to the pot over low heat. Mash with a whisk, fork, potato masher, or pastry cutter. Once mashed, pour in the sugar/spices/coconut milk mixture. Stir until incorporated and smooth.
Pour the potato mixture into the prepared baking dish. Sprinkle with the candied pecans. Then add a layer of coconut. Finish with a layer of mini marshmallows. Cook for about 25 minutes, or until the marshmallows are toasty and slightly browned, and the casserole is warmed through. Enjoy!