1

Preheat oven to 180°C. Lightly spray a 20cm square cake tin with oil and line base and sides with baking paper, extending paper 2cm above pan edges.

2

Combine ⅔ cup flour, polenta, baking powder and a pinch of salt in a medium bowl. Set aside.

3

Whisk eggs and egg white in a separate bowl until combined. Transfer 1 tablespoon beaten egg mixture to a cup and stir in 2 teaspoons water. Set aside both egg mixtures.

4

Using an electric mixer on low speed, beat butter and ¼ cup sugar in a small bowl until creamy. Beat in egg and water mixture, then add flour mixture and beat until combined. Using damp hands, press mixture evenly. over base and 1cm up sides of prepared tin. Bake for 20 minutes, or until golden.

5

Meanwhile, to make filling, place remaining 1/3 cup of flour and 1/2 cup of sugar in a medium bowl. Whisk in remaining egg mixture, lemon rind and juice and lime rind and juice until well combined.

6

Reduce oven temperature to 150°C. Pour filling over hot crust in tin. Bake for 20 minutes or until filling is set. Cool in tin on a wire rack. Refrigerate for at least 1 hour or until cold. Using baking paper lining, lift slice from pan. Dust with icing sugar and cut into 16 squares.