Preheat oven to 410 degrees F (210 degrees C).
In a large bowl, beat the yolks of the Egg (3). Then, mix in the Unsweetened Pumpkin Purée (80 gram), Brown Sugar (20 gram), and Maple Syrup (1 1/4 teaspoon) until they are well combined.
Pour the Vegetable Oil (40 milliliter) and Water (60 milliliter) into a beaker and gradually pour it into the egg yolk mixture while continuously whisking.
Sift in the Cake Flour (65 gram), Baking Powder (1 teaspoon), and Ground Cinnamon (1/2 teaspoon). Mix well and set aside.
Using an electric mixer on low speed, beat the egg whites until they are white and frothy. Then, add in 1/3 of the Caster Sugar (50 gram) and increase the mixer's speed to medium. Continue to beat the egg whites, adding the remaining sugar a little at a time.
Beat until stiff peaks form.
Add the meringue 1/3 at a time to the mixture in Step 4. Gently fold it in until well combined.
Add in the Roasted Pumpkin Seeds (2 1/2 teaspoon) and fold to combine.
Transfer the batter to a chiffon cake pan, and run the chopstick through the batter to level it.
Bake in preheated oven for 15 minutes, then turn the oven down to 355 degrees F (180 degrees C) and bake for another 10 minutes. Check if the cake is done by sticking a toothpick into the cake. If the toothpick comes out clean, it is ready.
Let the cake cool before removing from the cake pan by inverting the pan onto a plate or decorating tray.
For the frosting, use an electric mixer on high speed to beat the Unsalted Butter (60 gram) until it is white and fluffy.
Add the Powdered Confectioners Sugar (2 1/2 teaspoon), Ground Cinnamon (1/2 teaspoon), Ground Ginger (1/4 teaspoon), and Ground Nutmeg (1/4 teaspoon). Mix well.
Mix in the 100% Pumpkin Purée (50 gram).
To get a smooth buttercream, add the Milk (1 tablespoon) and mix until well combined.
Once the chiffon cake has cooled completely, frost the cake with the buttercream.
We are going to make the chiffon cake look like a cute pumpkin. For the pumpkin stem, break a Walnut (1) in half. Insert it to the top. Use the Pumpkin Seeds (to taste) to form leaves near the stem. Use the White Chocolate Chips (2) as the eyes and draw on irises using black Royal Icing (to taste).