In a large bowl use an electric mixer to combine the butter, coconut sugar, eggs, agave nectar, and vanilla.
Add the hazelnut flour, baking powder and salt.
Mix again to combine.
Line an 8×8 square pan with parchment paper.
Transfer the batter to a square pan and spread in an even layer.
Bake the cake in the oven for 20 – 25 minutes until a toothpick comes out clean.
Allow the cake to cool for 5 minutes, then transfer to a cooling rack and allow it to cool completely before frosting. I find it easiest to slide a knife around any edges touching the pan and pull up the parchment paper edges.
While the cake is cooling, make the frosting. Use an electric mixer to cream the butter in a medium bowl for about 1 minute.
Add the cocoa and agave nectar. Mix again until combined.
Once the cake is cool, spread the frosting out on the top of the cake in an even layer.
Sprinkle the top of the cake with chopped hazelnuts and enjoy!