Preheat your oven to 180°C (356°F) and line two 5.5-inch baking tins with baking paper.

Combine almond milk and apple cider vinegar in a large bowl and let sit for 5 minutes.

Add vegetable oil, caster sugar, and vanilla extract to the wet mixture and whisk until smooth.

Sift together flour, cocoa powder, baking powder, baking soda, and salt in a separate bowl.

Gradually mix the dry ingredients into the wet ingredients until just combined.

Divide the batter evenly between the two prepared tins and bake for approximately 45 minutes.

Allow cakes to cool in the tins for 10 minutes, then transfer to a cooling rack.

Beat icing sugar and softened vegetable shortening together until fluffy, then add vanilla.

Blend in melted chocolate and cocoa powder into the buttercream mixture until well combined.

To assemble, frost the top of one layer with buttercream, place the second layer on top and frost the entire cake.