A delicately flavored sponge cake with fragrant coffee buttercream frosting.
Preheat your oven to 350°F (180°C/ 160°C fan/ Gas mark 4) and grease or line two 9-inch round cake tins.
Mix the instant coffee granules with 1 tablespoon of boiling water and set aside to cool.
In a small bowl, mix the ground flax seeds with 6 tablespoons of cold water and set this aside too. After 5 minutes, it should be thick and "gloopy".
In a separate, large bowl, cream together the butter and sugar until smooth. Add in your flax seed mixture and stir again.
To the same bowl, add in the flour, baking powder and plant-based milk. Fold it all in using a figure of 8 motion with your spoon.
Add your cooled coffee mixture and fold it into the cake batter.
Divide the cake batter between the two tins and use the back of your spoon to make sure they're evenly spread in the tins.
Bake for 30 minutes, or until a toothpick through the center comes out clean. Leave the cakes in the tins for 10 minutes, then flip them out onto a cooling rack and leave them to cool completely.
Mix the coffee granules with 1 teaspoon of boiling water and set aside to cool. If you want your coffee cake to taste a bit stronger, you can double this amount to 2 teaspoons.
In a large bowl, mix together the vegan butter and powdered sugar. You can use an electric mixer for ease but doing it by hand will work fine too!
Add in your cooled coffee and gently stir it in.
Place your first cooled cake onto a plate, board or cake stand. Using a palette knife or spatula, spread a thick later of frosting over the top.
Add your second cake on top and spread another thick layer of frosting on top of that. You can use any leftover frosting to pipe buttercream swirls around the top if you wish.
Sprinkle the chopped walnuts and sugar crystals around the edge of the cake if using.
Allow the cake to sit at room temperature for 1 hour so the frosting becomes firm. Then cut into 16 slices and enjoy!
*Store, covered, in the fridge for up to 5 days.