1 Preheat oven to 180ÂșC. Line base and sides of a 30 x 20cm lamington tin with baking paper. Using an electric beater, cream butter, sugar and vanilla until light and creamy. Sift over flour and stir with a wooden spoon until combined. Press mixture into base and 2.5cm up sides of prepared tin. Bake for 10 minutes or until starting to brown around edges; let cool.
2 Put eggs, extra sugar and flour, milk, rind and juice in a bowl and whisk until well combined. Pour mixture over base. Bake for 20-25 minutes or until just set. Stand tin on a wire rack to cool. When cold, cut into squares and dust with icing sugar.