Preheat your oven to 350°F (175°C) and grease two 6-inch cake pans with baking spray or softened butter. Dust them lightly with flour.

In a large mixing bowl, whisk together the flour, baking powder, pumpkin pie spice, and salt until evenly combined.

In another bowl, mix together the granulated sugar, light-brown sugar, melted unsalted butter, vegetable oil, pumpkin puree, and eggs. Blend until smooth.

Gradually add the dry mixture to the wet ingredients, mixing gently until just combined.

Divide the batter evenly between the two prepared pans and bake for 35-40 minutes until a toothpick comes out clean.

Once baked, let the cakes cool in the pans for about 10 minutes then transfer them to wire racks to cool completely.

Whisk the egg whites and sugar together in a bowl over a hot water bath until the sugar dissolves. Whip until stiff peaks form.

Gradually mix in the room temperature unsalted butter and instant espresso powder until the buttercream is light and fluffy.

Cut each cooled cake layer in half horizontally, creating four layers. Stack two layers on a serving platter with buttercream in between.

Crumb coat the entire cake with a thin layer of buttercream, then apply a thicker layer on top and around the sides.

Finish with decorative swirls of buttercream.