Preheat the oven to 175C and grease and line a spring bottom pan with baking paper. My pan was 18cm.
Using a food processor or mini chopper, process the ingredients for the middle layer until a little more course than nut flour consistency. I used a mortar and pestle, or the back of a cake roller. Set aside.
For the streusel layer, process the hazelnuts, oats, sugar, and salt until medium chunky. Transfer to a bowl. Using your fingers, pinch together the nut mixture, butter, and flour to a crumbly mixture. Set aside.
For the cake, start by melting the butter in a small sauce pan. Stir in the milk and both sachets of Society Coffee Hazelnut Cappuccino powder and set aside to cool.
Whip the eggs and sugar white and fluffy. Sift and fold in the remaining ingredients.
Carefully fold in the butter mixture and fold in to a smooth batter.
Transfer half the batter to the prepared pan. Top with the middle hazelnut layer. Spread the remaining batter onto and finish with crumbling the streusel on top.
Bake for 40-45 minutes in the bottom of the oven so that the streusel do not burn. Use a cake tester to see if it's done.
