Lemon shortcake

Something a bit unusual for me- made for my mate down at Grays in Clarendon St. A dense but crumbly shortcake with lemon passionfruit frosting. Quite tasty and good mouthfeel. Super easy to make:
125g butter
1/4 cup caster sugar
1 egg
2 cups flour
1 tsp baking powder
Cream butter and sugar, beat in egg.
Mix in dry ingredients to form a crumbly mixture. Press into a 20cm square pan and bake 20 minutes.
Frost with your fave icing- I used 1 cup icing sugar, 2 tbsp butter, 2 tbsp lemon juice and a dash of passion fruit essence. Top with coconut flakes.