Preheat your oven to 375 degrees.
Wash your sweet potatoes and poke the skins several times with a fork. Wrap the potatoes in tin foil, twisting the ends. Bake on a baking sheet for 45-50 minutes, until potatoes are tender.
Give the potatoes some time to cool, then cut them in half and scoop out the potato from the skins. Be sure to leave a nice buffer for yourself between your scooping and the skin of the potato. Add the scooped potato into a large bowl. Use your hand masher to mash your sweet potato slightly. Add butter, milk, brown sugar, vanilla, and cinnamon. Stir well to combine. Fill the sweet potato skins back in with the sweet potato mixture.
Top with miniature marshmallows. To toast the marshmallows, place the potatoes back into theoven with the broil setting on low. Watch carefully, they toast up quickly, in about 1-2 minutes.