How to Make It
Make the cake Preheat the oven to 350°. Butter two 9-inch round cake pans and line the bottoms with parchment paper. Butter the paper and dust with flour, tapping out the excess.
In a medium bowl, whisk the 3 cups of all-purpose flour with the cinnamon, ginger, baking soda, baking powder and salt.
In a large bowl, using a hand mixer, beat the eggs with the brown sugar, pumpkin and oil at medium-high speed until blended. At low speed, beat in the dry ingredients.
Scrape the batter into the prepared pans and bake in the center of the oven for about 40 minutes, until a toothpick inserted in the center of the cakes comes out clean. Let the cakes cool in the pans for 30 minutes, then invert onto a rack to cool completely. Peel off the parchment paper.
Meanwhile, make the frosting In a large bowl, using a hand mixer, beat the butter with the confectioners sugar, vanilla and a pinch of salt until smooth. Add the mascarpone and beat at high speed just until smooth; do not overbeat. Refrigerate the frosting until just set, about 30 minutes.
Set 1 cake layer on a platter. Spread 3/4 cup of the frosting on top and cover with the second cake layer. Spread a thin layer of frosting all over the cake and refrigerate until set, about 15 minutes. Spread the remaining frosting over the top and side of the cake. Refrigerate until firm, at least 30 minutes, before serving.