Preheat oven to 425 degrees F.
Pierce the sweet potatoes with a fork and bake until tender, about 1 hour. Roast the bananas, with the skins on, for the last 15 minutes of cooking time. When cool enough to handle, peel the potatoes and bananas, and transfer to a food processor. Pulse until the potatoes are chunky.
Add the butter and maple syrup, puree until smooth. Add the cinnamon, pumpkin pie spice and salt; puree to combine. Transfer to a shallow baking pan and smooth out the surface with a spatula.
In a skillet, cook the pecans in butter over low heat and sprinkle with salt. Saute until well-coated, stirring occasionally, for about 5 minutes. Transfer the pecans to paper towels to drain. Arrange pecans on top of puree and sprinkle with brown sugar. Bake at 300 degrees F until heated through, about 20 minutes.
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