For the sponge: Firstly preheat the oven to 180C/160C Fan/Gas Mark 4, and line a muffin tin with 6 large cupcake cases.
Whisk all the dry ingredients together in a large bowl. Then add all the wet ingredients and whisk together until a smooth batter forms. Divide evenly between the cupcake cases and bake for 24 minutes. Leave in the muffin tin to cool for at least 30 minutes to cool, as they will be extremely soft. Then remove from the tin and place on a cooling rack, to cool completely.
For the buttercream: Whilst the cupcakes are cooling, place the raspberries into a food processor and blitz to a puree. Then strain through a sieve, and discard the seeds.
Place the remaining raspberry juice into a small pan and place over a medium heat. Cook stirring constantly until the raspberry juice has thickened to a pure consistency and has reduced considerably. Then set aside to cool completely.
Place the vegan butter in a large bowl and using an electric handwhisk, whisk until creamy. Then add the icing sugar and whisk on a low speed until combined, then increase to a high speed and whisk for 2-3 minutes. Finally add the cooled raspberry puree and fold to combine. Place the buttercream into a piping bag fitted with a star tip. Pipe swirls onto the cooled cupcakes and top with a raspberry.