Preheat oven to 160°C. Line a 19cm square tin with baking paper that comes up above the sides of tin for easy removal. Set aside.
Place all base ingredients into TM bowl and blend 15 sec/speed 8. It should resemble sand. Add a few seconds if your butter is too cold.
Press into prepared tin and bake until just golden about 20 minutes.
Meanwhile, without washing, place the filling ingredients into TM bowl and blend 30 sec/speed 10.
Pour onto warm base and return to the oven until edges are just browning and centre is wobbly around 15-20 minutes.
Cool slightly before dusting liberally with icing sugar.