Heat the oven to 160C/fan 140C/gas 3. Butter and line the bottom of a 20cm round cake tin. Put all the cake ingredients in a large bowl and beat for about 2 mins until smooth. Bake for about 50-60 mins, or until risen and springy to the touch. Leave to cool briefly in the tin, then turn the cake out and cool on a wire rack. If the cake peaks a bit, slice off the top to level it.
For the filling, cut the cake in half and sandwich back together with the lemon curd. Brush the top of the cake with a little more lemon curd. Roll out the icing and cut into a 20cm round. Carefully place on top of the cake, press down gently, smoothing it with your hands. Stick the lollipops into the icing at different levels, and the appropriate number of candles, then scatter on some jelly sweets or Smarties. The cake will keep in an airtight container in a cool place for up to 3 days.