In a small bowl, mix coffee and boiling water. Then add flaxseed and mix well. Set aside for 5-10 minutes.
In a separate bowl, mix flour, sugar, salt, and baking powder.
Then add oil, plant milk, and vanilla to your flaxseed mixture.
Pour your wet mixture over your dry ingredients. Mix until combined but do not overmix.
Brush all the inner sides of a cake tin with oil. Then cut out a circle-shaped baking paper and place it in the bottom of your cake tin.
Transfer to a lined cake tin. Smooth out the top.
Bake at 374°F / 190°C for 50-55 minutes until a wooden skewer inserted in the middle comes out clean.
In the meantime, prepare your icing by mixing sugar, butter, and cocoa powder in a small bowl. You will need to use a spoon to press down the butter against the sides of the bowl to get it to melt and mix with the other ingredients. Mix vigorously until fully combined.
When your icing is ready, cover with cling film and place in the fridge for 10-15 minutes.
When your cake is baked, remove it from the oven and let cool completely.
Then cover with icing and sprinkle with roasted hazelnuts and cocoa.