Apple coffee cake

Pre-heat the oven to 175°C/350°F. Grease a deep, 20cm round cake pan and line the bottom with waxed paper. For the cake: beat butter and sugar until light and creamy. Gradually add the beaten egg, beating well after each addition. Add the vanilla extract. Fold in the flour, then the yogurt, and stir until smooth. Spoon the batter into prepared pan and smooth the surface. Arrange the apple slices evenly over the mixture in a circular pattern, starting in the center. Sprinkle with the cinnamon and the sugar (the topping ingredients). Melt the butter and drizzle over the top. Bake for 1 hour or until skewer comes out clean when inserted into the center of the cake. Leave in the pan for 30 minutes before unmolding – set on a wire track to cool. If desired, combine a little extra sugar and cinnamon and sprinkle over the apples.