How to Make It
In a medium bowl, using an electric mixer, beat the mascarpone and cream cheese until smooth. Add the confectioners' sugar and beat until incorporated. Beat in the vanilla. Cover and refrigerate the frosting until it is firm enough to spread, about 1 hour.
Preheat the oven to 350°. Line 16 muffin cups with paper liners. In a large bowl, whisk the rice flour with the tapioca flour, baking powder, baking soda, salt, ginger, cinnamon, allspice and nutmeg. In a medium bowl, whisk the brown sugar with the granulated sugar, vegetable oil and eggs. Add the wet ingredients to the dry ingredients and whisk until smooth; whisk in the pumpkin puree.
Spoon the batter into the prepared muffin cups. Bake for about 25 minutes, until the cupcakes spring back when gently pressed. Transfer the cupcakes to a rack and let cool completely.
In a medium saucepan, spread the sugar evenly and cook over moderately low heat, shaking the pan to keep the sugar in an even layer. Cook, swirling the saucepan occasionally, until the sugar is melted and a deep-amber caramel forms. Slowly add the cream (be careful, the caramel will boil vigorously) and cook, whisking, until smooth. Transfer the caramel to a heatproof bowl and stir in the salt. Let cool to room temperature.
Frost the cupcakes and drizzle with the caramel sauce. Garnish with the crystallized ginger and serve.