In the bowl of an electric mixer fitted with the paddle attachment, beat the sugar and eggs together on medium-high speed until light and fluffy, about 5 minutes. Add the oil and vanilla and beat on medium until combined, about 30 seconds. Add the pumpkin filling and mix until combined, about another 30 seconds.

In a medium bowl, whisk together the flour, baking powder, cinnamon, ground ginger, nutmeg, and salt, and with the mixer on the lowest speed, gradually add to the pumpkin/egg mixture.

Evenly distribute batter into the prepared pans, smooth with a small offset palette knife and place in the center of the middle rack of the oven, about 2 inches apart. Bake until a knife or toothpick inserted into the center comes out clean, about 25 minutes. (Mine took 23).

Let pans cool on a wire rack 10 minutes, and then invert cakes onto rack and cool them completely.

Using a whisk, mix the sugar, brown sugar, cornstarch, cinnamon, ginger, and salt in a medium sized bowl until no lumps remain.

Blend in the pumpkin, whipping cream, sour cream and eggs.

Preheat the oven to 350 degrees F. Line a half sheet pan with parchment paper and set aside.

Bake for about 15 minutes, until lightly golden brown on top.

Place the marshmallows on a cookie sheet lined with parchment paper and sprayed with nonstick cooking spray. Place on the middle rack of the oven, and broil the marshmallows until golden brown on top, about 30-60 seconds. Keep your eye on them!

Remove the pan from the oven and gently turn the marshmallows over and broil them again until they are golden brown on the other side.

In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and powdered sugar and beat on low until blended. Add the vanilla and mix on medium speed for about three minutes

With the mixer on low speed, add the marshmallow cream and (cooled) toasted marshmallows, and mix for about one minute.

In the bowl of a stand mixer fitted with a paddle attachment, cream the butter for about 2 minutes. This will soften the butter without it having to be warm.

With the mixer on low speed, gradually add the sifted powdered sugar, one cup at a time, mixing a little in between each addition.

With mixer on medium speed, add whipping cream, vanilla and salt.

Turn the mixer to medium-high speed and beat for an additional 5 to 7 minutes. The frosting will become lighter in color and texture.

Before spreading on your cake, spend a couple minutes mixing the buttercream by hand with a wooden spoon to push out the air pockets.

Slice each cake layer in half horizontally, so you have six cake layers.

Place the first layer on your cake board, cut side up (so bottom of the cake layer is touching the board), and spread about 3/4 cup of the pumpkin pie filling on top, followed by about 1/2 to 3/4 cup of shortbread crumbs. Gently pat the crumbs into the filling with your hands to set them in place.

Place the next cake layer on top and cover with about 3/4 cup marshmallow filling.

Repeat step 2 and 3 until you get to your final cake layer. Place the final cake layer, top side down, on top of the final layer of pumpkin pie filling and shortbread crumbs.

Cover the cake with a thin layer of frosting and chill for 10 to 15 minutes in the freezer. This crumb coat will set the crumbs in place.