2 to 2 1/2 pounds sweet potatoes (about 4 to 5 medium)
1/2 cup coconut milk (or whole milk or cream)
2 to 3 tablespoons packed brown sugar
2 tablespoons unsalted butter
1 1/2 teaspoons vanilla bean paste (or pure vanilla extract)
Ground cinnamon, to taste
Kosher salt, to taste
Chopped fresh parsley leaves or coconut flakes, for garnish (optional)
Arrange a rack in the middle of the oven and heat to 425°F. Line a baking sheet with aluminum foil.
Pierce the sweet potatoes a few times with a sharp knife. Place them on the baking sheet and roast until tender and a knife easily pricks through, 45 minutes to 1 hour. Set aside to cool until cool enough to handle.
Halve the potatoes lengthwise, scoop of the flesh, and run the flesh through a potato ricer or food mill into a large bowl.
Meanwhile, combine the coconut milk, brown sugar, butter, vanilla bean paste, a few dashes of cinnamon, and a generous pinch of salt in a saucepan and cook over medium heat, stirring occasionally, until the butter is melted and sugar dissolved. Reduce the heat to low and keep warm.
Add the warmed milk mixture, a few tablespoons at a time, into the potatoes, and beat with an electric mixer on high speed until smooth and fluffy. (You may not use all of the milk mixture.)
Taste and adjust seasonings, adding more sugar, cinnamon, or salt as needed. Serve immediately. Garnish with the parsley or coconut flakes if using.
Make ahead: This recipe can be made ahead and stored in the refrigerator for up to 2 days. To reheat (or keep warm), place the bowl of potatoes over a bowl of simmering water, stirring occasionally.
Storage: Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.