1. Start with the streusels – add flour, brown sugar, and cinnamon to a bowl and mix to combine. Add the margarine and rub everything between your fingers to create different-sized streusels. Add the sliced hazelnuts and mix in. Set aside.

2. Preheat the oven to 350°F (175°C). Line a 9-inch (23cm) springform tin with baking parchment and grease lightly. Set aside.

3. Separate the eggs. Whisk the egg whites until stiff peaks form and set aside. Add the egg yolks and brown sugar to a large bowl and mix for 2-3 minutes until light and fluffy. Add the softened margarine and vanilla extract and mix until well combined. In another bowl mix ground hazelnuts, almonds, spelt flour, baking powder, cinnamon, and salt. Add to the large bowl along with the plant-based milk and mix well. Fold in the whisked egg whites gradually and gently to make sure you keep as much volume as possible. Pour the batter into the prepared baking tin and smooth out the top. Sprinkle the streusels on top and bake for about 60-70 minutes – or until a wooden skewer inserted into the center of the cake comes out clean. Take it out of the oven and let cool down completely on a wire rack inside the baking tin.