Preheat oven to 350 degrees F. Grease 3 (6-inch) round cake pans or 2 (8 inch) round cake pans. Line with parchment paper, then butter/spray with cooking spray.In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, ginger, cardamom, all-spice, nutmeg, and pepper. In the bowl of a stand mixer (or use a hand-held mixer) beat together the canola oil, sugar, vanilla, eggs, and pumpkin until combined. Gradually add the dry ingredients until smooth and no lumps remain in the batter.Pour the batter among the cake pans and bake 35-40 minutes, until the tops are just set, and no longer wiggly in the center. Remove and let cool 10-15 minutes, then run a knife around the edges of the pan and turn the cakes out onto a cooling rack. Cover and let the cakes cool completely before assembling.To make the buttercream frosting. Add 2 sticks butter to a skillet, set over medium heat. Allow the butter to brown lightly until it smells toasted, about 2-3 minutes. Stir often. Remove from the heat and transfer the butter to the mixing bowl, let cool until it's room temp. Add the remaining stick of room temperature butter and the cream cheese to the bowl. Then add the powdered sugar and maple syrup. Beat together until light and fluffy. Add the vanilla and beat until combined. If the frosting feels too loose, add powdered sugar to thicken. To assemble. Place one cake layer on a serving plate. Spread 1/3 of the buttercream over the cake. Repeat with the remaining 2 cake layers. Be careful not to overfill your layers or the cake will be hard to slice. Frost the outside of the cake. Chill 30 minutes. Serve, or store in the fridge for up to 4 days. Decorate, as desired with mini pumpkins and melted chocolate.