01 -
Line a 9x13 inch baking pan with parchment paper and coat with nonstick cooking spray.
02 -
Set oven temperature to 350°F (175°C) and allow to preheat.
03 -
In a large bowl, whisk together all-purpose flour and icing sugar.
04 -
Add cold butter cubes and cut into flour mixture with a pastry cutter or fingertips until pea-sized crumbs form. If mixture is too dry, blend in cold water 1 tablespoon at a time.
05 -
Press crust mixture evenly into the prepared pan. Bake in preheated oven for 10 minutes. Remove from oven and set aside.
06 -
Melt unsalted butter in a medium bowl. Whisk in brown sugar until smooth, then incorporate eggs one at a time, whisking well after each addition. Blend in white vinegar and vanilla extract. Stir in raisins if desired.
07 -
Pour the filling evenly over the baked crust. Return pan to oven and bake for 25 to 30 minutes, until filling is mostly set with a slight jiggle at the center.
08 -
Allow pan to cool to room temperature. Refrigerate for several hours until fully set.
09 -
Cut into squares and serve chilled or at room temperature.