To a medium bowl, add the milk and vinegar, and give it a mix. You will see it starts to curdle, by doing this we are creating a vegan buttermilk.

Place a sieve over a large bowl, sift all the dry ingredients through it. Mix together.
To the same large bowl, add the buttermilk and all wet ingredients. Mix until there are no lumps left, but make sure to not over mix.

Grease a (20 cm) round cake pan with oil and line the bottom with a cut-out round piece of parchment paper.
Put in the cake batter and bake in the oven for 30 - 35 minutes at 180°C.

Meanwhile, make the frosting. To a large bowl, add the butter, sift in the cacao powder, and add the vanilla, and mix with an electric or hand mixer until smooth and creamy.
Alternate between adding sifted powdered sugar and plant-based milk to the bowl, until well combined.
Using a spatula, fold in the melted chocolate, make sure to let it cool off a little bit before adding.

Once your cake is done baking, let it cool off for 10 minutes in the cake pan before transferring to a cooling rack to let it cool off completely.
If you like, you can level your cake with a serrated knife to create a flat surface for stacking the cakes on top of each other.

Using a spatula or butter knife, spread out a thick layer of frosting on one of the cakes.
Place the second cake on top and frost with the leftover frosting, you can even create a pattern if you like.
Decorate the chocolate cake with berries of your choice and some mint leaves, and enjoy!

Notes
Storage: best if enjoyed immediately. The cake can be stored in the fridge for up to 3 days.
Variations: top the cake with any fruits of your choice, or add some nuts for example.