For the Victoria sponge, cream the butter and sugar in an electric mixer, then mix in the lemon zest. With the machine running, slowly add the eggs and beat until well combined. Fold in the flour, pistachios and baking powder. Pour the mixture into the cake pan and bake for 30 minutes or until a skewer comes out clean. Remove from the oven and allow to cool for 10 minutes before inverting the sponge onto a wire rack to cool completely.