Pre-heat the oven to 180°C / 160°C fan assisted / gas mark 4 / 350°F.
Line a 12-hole regular muffin tin with cupcake cases.
Make the chia egg by combining the ground chia seeds with water in a small bowl. Stir, and set aside for about 5–10 minutes until the mixture thickens into a gel-like consistency.
In a large mixing bowl, sift together the gluten-free flour blend, cocoa powder, baking powder, bicarbonate of soda, and salt. Set aside for a moment.
In a separate bowl, whisk together the olive oil, soft light brown sugar, thickened chia mixture, plant-based yoghurt, apple cider vinegar, and vanilla extract. Mix until smooth.
Pour the wet mixture into the dry ingredients and mix until the cake batter is thick and everything has fully incorporated
Spoon the batter evenly into the prepared cupcake cases, smoothing down the top of the batter so the cupcakes bake evenly. Bake for 25 minutes, or until a skewer inserted into the centre of a cupcake comes out clean. Immediately transfer the cupcakes to a wire rack to cool completely before applying the buttercream frosting.
To make the buttercream, mix the plant-based butter in a large bowl with the icing sugar until soft and creamy.
Sift in the cocoa powder, then add the vanilla extract and salt. Start mixing on low speed to avoid a sugar cloud, then increase to medium-high and beat until fluffy and smooth. If your buttercream is too soft after mixing then place in the fridge for 30 minutes – 1 hour to firm up.
Once the cupcakes are completely cool, pipe or spread the chocolate buttercream generously over the top. You can finish with a sprinkling of dairy-free chocolate curls if you like.
To make the chocolate curls take the chocolate bar and, using a vegetable peeler, peel the chocolate from the thin edge. It will curl up as it falls away.