3 tbsp strawberry milkshake powder
250g/9oz caster sugar
pinch salt
250g/9oz self-raising flour, sieved
250g/9oz unsalted butter, softened
300g/10陆oz unsalted butter, softened and cubed
250g/9oz free-range eggs, weighed in their shells (about 4 medium eggs)
3 medium free-range egg whites