How to Make It
Preheat the oven to 325° and line the bottom of a deep 81/2-inch cake pan with parchment paper.
In a medium bowl, whisk together the flour, cinnamon, cardamom, nutmeg, and salt and set aside.
In a small frying pan over medium heat, toast the hazelnuts until fragrant, about 3 minutes. Transfer half of the nuts to a small food processor and pulse until a coarsely ground flour forms. Roughly chop the remaining hazelnuts over a cutting board into small sized pieces. Add both the hazelnut meal and loosely chopped pieces to the bowl of dry ingredients.
In a large bowl, whisk together the eggs, sugars, coconut oil, pumpkin puree, and vanilla until very smooth. Gently fold in the dry ingredients until incorporated. Using a spatula, scrape the batter into the parchment lined pan. Smooth out the surface of the cake batter with the spatula and sprinkle the remaining two tablespoons of demerara sugar evenly over the top.
Bake for 45 minutes until a toothpick inserted in the center comes out clean. The top of the cake should be crispy and cracked from the scattered sugar coating. Let the cake cool for 15 minutes before removing it from the pan. Gently peel off the parchment paper from the bottom and let stand.
Mix the confectioner's sugar, espresso, almond milk, maple syrup, and salt together until smooth. Drizzle over the cake and serve.