Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper.
To make the batter: In the bowl of a stand mixer fitted with the paddle attachment, add the butter, light brown sugar, maple syrup, and vanilla extract. Mix on low until combined and there’s no butter chunks.
Add the eggs, milk, and sour cream and mix on low until combined.
Add the all purpose flour, cinnamon, allspice, cloves, baking powder, and sea salt in that order. Mix on low until combined into a smooth batter. Transfer the batter to the prepared baking pan and spread evenly.
Bake for 27 to 30 minutes or until a toothpick inserted in the center comes out clean. Allow to cool completely in the baking pan.
To make the frosting: In the bowl of a stand mixer fitted with the paddle attachment, add the butter, powdered sugar, light brown sugar, and vanilla extract. Mix on low and add in the heavy whipping cream. Continue to mix until combined and then speed the mixer up to high and mix for 2 to 3 minutes or until light and fluffy.
Transfer the frosting to the cake and spread evenly.
Add 9 chocolate maple leaves to the top of the cake (3x3) so there’s one on each piece when cut. Cut the cake into 9 slices.
Store extra in an airtight container in the fridge.