This recipe is from Tammy Donroe Inman, author of Wintersweet: Seasonal Desserts to Warm the Home.
Preheat the oven to 350°F. Grease a 9-inch cake pan. Line the bottom of the pan with parchment paper; grease and lightly flour the pan.
In a large bowl, whisk together the maple syrup, vegetable oil, brown sugar, butter, and vanilla. Whisk in the eggs, one at a time. Add the flour, baking powder, baking soda, salt, and pumpkin pie spices, and mix well with a wooden spoon. Stir in the parsnips until well combined. Spread the batter evenly in the prepared pan.
Bake 35 to 40 minutes until the center is fully puffed and springy, and a toothpick inserted into the center comes out clean. Remove the cake from the oven and let it cool completely on a rack. Just before serving, set the cake on a pretty plate and arrange clean leaves on top. Sift powdered sugar evenly over the cake. Carefully remove the leaves.