Preheat the oven to 350 degrees. Peel and chop the potatoes into small cubes. Spread the potatoes out onto a baking sheet in an even layer (this may take two baking sheets depending on how big yours are). Drizzle the olive oil over the potatoes, and season with a pinch of salt. Toss to combine, then bake for 30-40 minutes, until soft.
When the potatoes are done baking, transfer them to a food processor. Add the maple syrup, almond milk, and vanilla. Blend for about 30 seconds, until you have a smooth consistency. Do not over blend because this could cause the potatoes to become gummy.
Remove the blade from the food processor, then stir in the chopped pecans.
Spray a 9x9 baking dish with non-stick spray, and transfer the sweet potatoes into the dish. Use a spoon to smooth out the top. Place the marshmallows on top in even rows so they cover all of the potatoes.
Place the dish in the oven and bake for another 10-15 minutes. Then, turn on the broiler and let the marshmallows brown. This will only take 3-4 minutes, so watch them closely because they will burn very quickly.
Once the marshmallows have turned slightly brown, remove from the oven and let it cool for at least 5 minutes before serving.