01 -
Line a 9x9-inch pan with foil or parchment, leaving overhang on two sides. Lightly coat with nonstick spray.
02 -
Arrange the graham crackers in a single tight layer on the bottom of the pan. Break pieces to fill gaps.
03 -
Scatter the mini marshmallows evenly over the graham crackers.
04 -
Combine caramel bits and milk in a microwave-safe bowl. Microwave for 1 minute, stir, then heat in 30-second bursts until smooth.
05 -
Pour the warm caramel over the marshmallows. Gently spread to the edges so the marshmallows are lightly coated and starting to soften.
06 -
Sprinkle chopped Butterfinger over the caramel and press lightly so the pieces stick.
07 -
Melt the semi-sweet chocolate in short microwave bursts, stirring until smooth. Drizzle over the top and add flaky salt if using.
08 -
Refrigerate for at least 1 hour, or until firm. Lift from the pan and cut into 12 bars with a sharp knife.