Preheat the oven to 350F. Grease and flour a round baking pan with detachable walls with butter and gluten-free flour. Pat the pan to remove the excess flour.
Mix together the almond milk and vinegar and let it curdle.
Combine the ground flax with water in a large mixing bowl and set aside for five minutes until it thickens.
Stir the baking soda into the almond milk mixture.
Add the almond milk, honey and sugar to the flax eggs and mix to combine. Whisk in the vanilla extract, butter, apple puree and salt.
Bring in the dry ingredients: add the almond meal, cacao powder and gluten-free flour mix. Whisk until everything is well combined. In case you consider the batter too thick, add an extra splash of milk.
Pour the batter into the prepared pan.
Bake for about 40-45 minutes. Check after 35 minutes and if a toothpick inserted in the middle of the cake comes out clean, remove it from the oven. The baking time may vary depending on your ingredients (if using gluten-free flour or not) and also on your oven.
Let the cake rest in the pan for 20 minutes. Use a butter knife to loosen the edges, remove the walls and transfer the cake to a wire rack to cool.
When it is completely cooled, use a serrated knife to cut it in two halves lengthwise.
To assemble the cake, spread 1/3 of the frosting on the bottom layer.
Cover with the other layer and press a bit so that everything is in place. Use the remaining mixture to frost the top of the cake. Decorate with chocolate flakes and place the cake in the fridge for about 1 hour before serving.
Cut into slices and enjoy!