1. Preheat oven to 350°F (175°C). Line a 13 x 9-inch (3.5 L) metal cake pan with parchment paper, leaving 1-inch (2.5 cm) extending over long edges for handles. Set aside.
2. Shortbread Crust: In a large bowl, with a hand mixer or stand mixer, cream butter and sugar until light and fluffy. Stir in flour in 2 additions until just combined. Press evenly into prepared pan and chill for 20 minutes. Bake for 20 minutes. Let cool in pan on rack.
3. Lemon Blueberry Filling: In a large bowl, whisk eggs, sugar, flour, lemon zest, lemon juice and salt until combined. Pour over cooled base; sprinkle with blueberries. Bake for 25-30 minutes, or until centre is set.
4. Let cool completely in pan on rack. Â Chill uncovered for at least 2 hours before serving. Slice into 16 bars of equal size; sprinkle with icing sugar and serve.
Tip:Â Substitute equal amounts of raspberries or blackberries for a flavour variation.
Tip:Â For a more traditional texture for the shortbread crust, use a food processor to process the granulated sugar to create a finer grain.