01 -
Line an 8-inch square tin with parchment paper, leaving overhang on two sides for lifting out the finished slab.
02 -
Warm 8 Bourbon biscuits on a microwave-safe plate for 8-10 seconds, just until the filling softens. Carefully twist or slide them apart into 16 halves and set aside.
03 -
Crush 450 g Bourbon biscuits into fine crumbs in a food processor, or seal them in a bag and crush with a rolling pin. Tip the crumbs into a large bowl.
04 -
Stir the melted butter, 1/2 cup condensed milk, and salt into the crumbs until evenly moistened. The mixture should hold together when squeezed.
05 -
Transfer the crumb mixture to the lined tin and press firmly into an even layer, especially around the corners.
06 -
Place the chopped milk chocolate and remaining condensed milk in a small saucepan over low heat. Stir constantly for 3-5 minutes, until smooth and glossy.
07 -
Spread the chocolate topping over the biscuit base. Arrange the split Bourbon biscuit halves on top, pressing lightly so they adhere.
08 -
Refrigerate for at least 3 hours, or overnight for the cleanest slices. Lift from the tin and cut into 16 squares with a warm, dry knife.