Preheat the oven to 180°C/ Fan 160°C/Gas 4. Butter 2 x 20cm sandwich cake tins and line the bases with baking parchment.
Place all the ingredients for the cake together in a large bowl and beat for a couple of minutes until just blended.
Divide the batter evenly between the 2 prepared tins. Bake for 20–25 minutes or until lightly golden. Leave the cakes to cool in the tin for 5 minutes, then transfer them to a wire rack.
To make the frosting, mix together the icing sugar, cream cheese, yogurt, orange and lemon juices and whisk until smooth. Place this in the refrigerator to chill and firm up while the cake cools.
When the cake is completely cool, use a palette knife to spread half the frosting on one cake. Place the other on top and ice with the rest of the frosting. Finish by decorating with a scattering of orange and lemon zests.