In medium size bowl mix 3 Tbsp sugar and 1 cup flour. Cut in butter until mixture is crumbly. Press crumbs firmly and evenly into bottom of an 8x8 inch square pan.
Bake for 15 to 17 minutes until just starting to brown.
In medium bowl, beat eggs. Stir together 2/3 cup sugar, 2 Tbsp flour and 1/4 tsp baking powder in small bowl and add to eggs (mix before adding to prevent flour from forming lumps). Beat in lemon zest and lemon juice.
Pour filling over baked pastry layer.
Bake for 20 minutes or until lightly golden around edges and center is set.
Cool completely on a wire rack.
Cut into 16-20 squares/bars.
Sift powdered sugar over top of bars and garnish with extra lemon zest.
Once cooled, store extras in the fridge for 7 days or freeze for longer (see blog post).