Preheat oven to 350F and grease & flour two 6" cake pans.
In a medium bowl, whisk together flour, pumpkin pie spice, baking powder, and salt.
In a large bowl, whisk together sugars, melted butter, oil, pumpkin, and eggs.
Add dry to wet and mix until just combined.
Divide batter evenly between prepared pans and bake until a toothpick inserted into the center comes out mostly clean (approx. 35-40 mins).
Cool in pans on wire rack for 10mins, then turn out onto wire racks to cool completely.
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a hot water bath on the stove and whisk constantly until the mixture is no longer grainy to the touch (approx. 3mins).
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.
Add espresso. Whip until smooth.**
Cut each layer of cake in half horizontally.
Place one layer of cake onto a serving plate or cake stand. Top with 1/2 to 2/3 cup buttercream. Repeat with remaining layers.
Crumb coat the entire cake (thin coat of frosting all over the cake). Chill for 30mins.
Use the remaining frosting to cover the outside of the cake. Decorate the top and sides with a swirl if desired (I used a large offset spatula to do this). Decorate with fondant pumpkins.
* Wipe your mixer bowl and whisk down with lemon juice or vinegar to make sure it is completely grease free and make sure there is no trace of yolk in your whites or your meringue will not stiffen.** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth. If it looks soupy, place it in the fridge for 20mins and rewhip.