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1
Preheat the oven to 350 degrees F. Poke the sweet potato with a fork a few times and bake until soft in the center, about 40 minutes.
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2
Let cool, then scoop out the flesh and puree in a food processor until smooth.
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3
Turn the oven down to 200 degrees F (to keep cooked waffles warm).
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4
Preheat a waffle iron to medium-high if there are settings (but it's ok if there aren't any).
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5
Whisk together the flour, baking powder, baking soda, cinnamon and salt in a medium bowl.
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6
Whisk together the buttermilk, 1/2 cup of the sweet potato puree, the oil, brown sugar, egg and egg white.
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7
Pour the buttermilk mixture into the flour mixture and gently stir until just incorporated (it's ok if there are lumps).
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8
Lightly brush the top and bottom of the waffle iron with oil, then fill each section about three-quarters of the way full (there should still be some waffle iron showing).
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9
Close and cook until the waffles are golden brown and slightly crisp, 6 to 10 minutes.
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10
Keep the waffles warm in the oven or covered with foil on a plate while you repeat with the remaining batter.
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11
Switch the oven to broil, and drizzle each waffle with a little syrup and 1/4 cup mini marshmallows.
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12
Broil until golden, 15 to 30 seconds.
