Preheat the oven to gas make 3/325oF/160oC/140oC fan then grease and line a 23cm (9inch) baking tin with non-stick baking paper. Dust the inside of the tin with flour then tap out the excess.
In a mixing bowl, cream together the golden caster sugar and the vegetable spread until smooth an fluffy. Beat in eggs, vanilla extract and yoghurt then sift in flour, cocoa and bicarbonate soda and stir until fully combined.
Spoon or pour mixture into the prepared tin and level the surface then bake for 45 minutes or until a cake tester inserted into the centre comes out clean. Place the tin onto a wire rack and cool for 20 minutes, then turn the cake out onto a rack to cool completely.
Make the ganache: once the cake has completely cooled, weigh out the dark chocolate in a heat resistant mixing bowl and set aside. In a saucepan, heat the double cream and bring to a boil. Ensure you do not leave the cream unattended as it will boil over. Pour the hot cream over the chocolate and ensure all the chocolate is submerged in the cream. Leave to stand for 4 minutes so the chocolate begins to melt. Stir the mixture until it is fully combined and the chocolate is smooth and glossy. Cover with cling film ensuring cling film touches the mixture.
Leave to stand until the ganache is at the right consistency for you, then using a palette knife spread the ganache all over the cake and create your desired effect.