Preheat your oven to 180c fan and line a regular sized loaf pan with baking paper.
Mix your soy milk and apple cider vinegar together to combine, then set aside for 5 minutes. This will allow the mixture to thicken and form your vegan buttermilk.
In a large mixing bowl, cream the sugar and olive oil together using a wooden spoon.
Once combined, whisk in the buttermilk mixture, then sift all of your dry ingredients apart from the cocoa powder.
Fold the wet and dry ingredients together to form a smooth batter, then divide this into two equal portions.
To one of your cake batters, stir in the cocoa powder and mix thoroughly until completely incorporated.
Transfer the mixtures into two individual piping bags and begin assembling the cake by piping alternate stripes of batter. You want to do this lengthways in the tin.
Repeat this process layering the batter, until all of the mixture is used up. Bake for approximately 40-45 minutes until golden and completely cooked through.
Remove your loaf cake from the oven and allow to cool on a wire cooling rack. Meanwhile, beat the butter until pale and fluffy, then gradually incorporate the icing sugar, cinnamon and cocoa powder.
To frost this cake, I love to pipe these little swirls on top for something slightly more fancy- but you can decorate how you like! Add some fresh fruit, or even little Easter eggs like I've done here and serve!