Once cool, smash up to a dust (you’ll need about half to top the cake – save the rest for sprinkling over ice cream).
To assemble the cake, place one sponge on a cake stand and spread with half the icing. Top with the other sponge, spread over the rest of the icing, then grate over the zest of the remaining lime.
Scatter over the brittle dust and decorate with a few edible flowers, such as violas, borage or herb flowers, if you feel that way inclined.
With a cup of tea on the side, this will make everyone who eats it extremely happy. Serve in a bluebell wood on a fallen tree, as you do.