Preheat oven to 350F and grease & flour two 6-inch 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 ingredients 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 10 mins, 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. 3 mins).

Place bowl on your stand mixer and whisk on medium-high until the meringue is stiff and cooled (approx. 5-10 mins).

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 with a thin coat of frosting and chill for 30 mins.

Use the remaining frosting to cover the outside of the cake. Decorate if desired.