Preheat your oven to 350°F and move a shelf to the upper 1/3 of your oven. Grease and flour 2 9 inch cake pans. Lining the bottom of the pans with parchment is recommended.
Start by sifting the spices, baking soda and powder, and flour into a small bowl. Set aside.
Separate the eggs. In a large bowl beat the egg whites until their stiff and fluffy, this is easiest with a stand mixer on medium high speed with the beater attachment.
In another bowl, beat together the pumpkin, oil, and sugars until well combined, add the egg yolks and vanilla and beat to combine until well mixed.
Fold the flour into the pumpkin mixture, once the flour is combined, add the egg whites half at a time, folding them gently into the batter. The batter should increase in volume and lighten in color.
Pour into prepared pans and bake for 35 - 40 minutes, or until the cake springs back to the touch, or a cake tester comes out clean.
Let cool 10 minutes in the pan, then flip onto a cooling rack and remove pan to allow faster cooling.
Make the Buttercream
Combine the mascarpone, butter, and vanilla in a large bowl and beat on medium speed until well combined and fluffy.
Add powdered sugar, 1 cup at a time, until it's all been added and the frosting is light and fluffy.*
Assemble the Cake
On a parchment lined surface, set one cake top down and pipe a border of buttercream around the diameter of the cake. Fill in the middle with a slightly shallower layer of buttercream.
Place the other cake layer, top down, onto the buttercream. Pipe buttercream around the sides and top and use and offset spatula to create an even layer of buttercream around the entire cake.
Chill the cake for 30 minutes.
Make your decorations while you wait. Cut marzipan leaves out with cookie cutters and use a paring knife or fondant tools to carve leaf ribs into them. Paint with a clean small paint brush and the powdered food color of choice.
Form 2 marzipan balls and press two ends slightly flat. Gently carve ribs from the top to the bottom of either flat end. Paint with orange powdered food dye.
Cut two small marzipan triangles for pumpkin stems and roll out a few thin vines for the pumpkin accents. Paint them brown and green.
Once the cake has chilled, apply a second layer of frosting, using your offset spatula to smooth an evening finished layer on.
Wrap the top half of your cake with a ring of parchment or wax paper. Move the cake onto a baking sheet if possible to catch sprinkles.
Using your fingers, gently press on sprinkles to the bottom half until coated to your liking.
Remove the parchment ring, create a pumpkin patch with gold sanding sugar and set the pumpkins with their stems and vines on top. Arrange leaves as desired.
Refrigerate until 30 minutes before you're ready to serve.
*You can add less or more powdered sugar to fine tune the stiffness of the finished buttercream.