Preheat oven to 375° and grease a mini muffin tin with cooking spray. Pierce sweet potatoes 3 to 4 times with a fork. Place potato on microwave-safe plate and microwave 15 minutes. If your potatoes aren't fork tender after 15 minutes, continue microwaving in 30 second increments.
When potatoes are cooked through, scrape filling into a large bowl and discard skin. Using a potato masher or fork, mash sweet potatoes until smooth. Add brown sugar, heavy cream, cinnamon, vanilla, and salt and whisk to combine.
On a lightly floured surface, roll out crescent dough, and pinch together seams. Cut into 24 squares and place in muffin tin cups.
Spoon a heaping tablespoon of sweet potato mixture into each crescent square, then top with mini marshmallows and bake until crescent pastry is golden, about 15 minutes. Add a pecan to the center of each bite and bake 5 minutes more. If using, brush pecans with maple syrup before serving.