Pre-heat your oven to 180°C/160°C fan.
Line a muffin tin (or two) with 14 cupcake/muffin cases.
Beat together the vegan margarine (180g), caster sugar (180g) and vanilla extract (1 tbsp) until combined and soft (the aim here is to ensure the margarine is soft so it's easy to mix in the other ingredients).
Finely grind the chia seeds (2 tbsp). I find this easiest in a spice grinder, but you can also do this in a pestle and mortar.
In a different bowl sift together the self-raising flour (270g), bicarbonate of soda (¾ tsp) and ground chia seeds.
Add the dry ingredients, the almond milk (135ml) and the vinegar (¾ tsp) to the margarine and sugar mixture and beat them together until combined.
As soon as the cake batter is ready, divide it between the 14 cupcake cases. Place into the oven and bake for 20-22 minutes until a skewer inserted into the centre comes out clean.
Once baked, remove the cakes from the oven. Leave the cakes to cool in the tin for about 10 minutes and then move them to a wire rack to cool completely.