Preheat the oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, ginger, nutmeg, and salt.
In a large bowl, whisk together the pumpkin puree, granulated sugar, brown sugar, vegetable oil, eggs, and vanilla until smooth.
Add the dry ingredients to the pumpkin mixture. Mix just until the flour is incorporated. Do not overmix
Divide the batter evenly between the prepared cake pans and smooth the tops.
Bake for 25 to 30 minutes, or until the cakes are set and a toothpick inserted in the center comes out clean or with a few moist crumbs
Cool the cakes in their pans for 10 minutes, then transfer them to a wire rack. Let them cool completely before frosting.
To make the frosting, beat the chilled mascarpone, heavy cream, powdered sugar, honey, and vanilla until smooth and thick enough to spread. Stop mixing as soon as the frosting reaches a creamy, spreadable consistency.
Place one cooled cake layer on a serving plate. Spread an even layer of frosting over the top.
Add the second cake layer and cover the top and sides with the remaining frosting.
Finish with a light sprinkle of cinnamon, toasted nuts, or a small drizzle of honey if desired.
Chill the assembled cake for about 30 minutes before slicing for cleaner layers.
