This recipe won first place in the 2017 Old Farmer’s Almanac Recipe Contest.
Place a 9x5-inch loaf pan in the freezer and allow to chill while preparing ice cream. Line a baking sheet with parchment paper and set aside.
In a skillet, melt butter over medium heat. Add pecans and toast lightly, stirring occasionally, for 2 minutes, or until fragrant. Sprinkle brown sugar over pecans and cook, stirring constantly for 2 to 3 minutes, or until sugar caramelizes and makes a glaze. Pour candied pecans onto prepared baking sheet in a single layer. Set aside and allow to cool and harden.
On a nonstick baking sheet, spread out marshmallows, making sure that they are not touching. Place baking sheet in oven and broil marshmallows until lightly browned. Set aside and allow to cool completely.
In a bowl, whisk together sweet potato purée, condensed milk, vanilla, cinnamon, ginger, and nutmeg until smooth.
In the bowl of a stand mixer, whip heavy cream for 3 to 5 minutes, or until medium peaks form. Using a spatula, very gently fold sweet potato mixture into whipped cream. Add candied pecans and marshmallows and gently fold a few times to fully incorporate.
Pour mixture into chilled loaf pan and cover tightly with plastic wrap, making sure that the plastic touches the ice cream to help in preventing crystallization. Place a second layer of plastic wrap over the top, sealing the edges of the pan, and place in freezer for at least 6 hours.