Preheat oven to 350F and line a baking dish with parchment paper (I used an 8x8 baking dish).
Beat egg and brown sugar until it’s nice and fluffy.
Add in pumpkin, oil, and vanilla and beat until fully combined.
Add in flour, pumpkin pie spice, sea salt, and baking soda and mix until fully combined.
Pour batter into baking dish and smooth out the top. Bake for 28-30 minutes or until a toothpick comes out clean(ish).
Let cool completely. While the cake cools, beat together cream cheese and butter. Add in maple syrup and pumpkin pie spice. Slowly add in powdered sugar as you mix until smooth. Spread frosting over cake and sprinkle cinnamon if you wish!