01 -
Line a 23 x 33 centimetre baking pan with parchment paper and lightly coat with non-stick spray. Preheat oven to 175°C.
02 -
In a large mixing bowl, combine flour and powdered icing sugar until evenly blended.
03 -
Incorporate cold, cubed butter using a pastry cutter or fingertips until mixture forms coarse crumbs with pea-sized butter pieces. If mixture does not hold shape when pressed, gradually blend in cold water until dough just comes together.
04 -
Transfer mixture to prepared pan and press evenly to form a compact base. Par-bake for 10 minutes.
05 -
While crust bakes, melt butter in a medium bowl. Whisk in brown sugar until smooth. Beat in eggs individually, then mix in white vinegar and vanilla extract. Gently fold in raisins, if using.
06 -
Pour filling evenly over hot crust. Return to oven and bake for 25–30 minutes, or until filling is set around the edges and retains a slight jiggle in the centre.
07 -
Allow to cool to room temperature, then refrigerate for several hours until fully set. Slice into squares before serving.