Preheat oven to 180°C. Lightly grease and line 2 x 20cm sandwich pans.
In a large bowl, using an electric mixer, cream butter and caster sugar together until creamy. Add eggs one at a time, beating well between each.
Sift self-raising flour and bicarbonate of soda together onto a piece of baking paper. Fold into creamed mixture, alternately with vanilla-bean yoghurt (unsweetened).
Divide evenly between pans, smoothing top. Bake for 20-25 minutes, until cooked when tested. Cool in pan for 3 minutes before turning onto a wire rack to cool completely.
Meanwhile, to make yoghurt icing; in a large bowl, whisk cream cheese, icing sugar and vanilla-bean yoghurt (unsweetened) together.
Spread ¾ cup of the icing onto the top of one cake. Remove the pulp from the passionfruit. Drizzle half over. Place second cake on top and spread with remaining icing, drizzle with passionfruit pulp and pistachios.
If liked, fill and top with plain vanilla yoghurt.Note