- PREHEAT oven to 350F. Spray 2 8 × 8-in. metal baking pans with oil and line each with overhanging parchment.
- STIR flour with salt in a medium bowl.
- BEAT butter with sugar in a large bowl, using a wooden spoon, until smooth, 1 min. Gradually stir in half of flour mixture, until just combined. Add remaining flour mixture, kneading with your hands, until dough forms a ball.
- DIVIDE dough in half. Press a portion of dough evenly into each prepared pan. Using a fork, prick dough all over.
- BAKE in centre of oven until golden, 28 to 30 min. Cool completely on a rack, about 1 hour.
- FOR CARAMEL: Melt Skor toffee bits with cream in a small saucepan over medium-high, stirring frequently, until smooth. Pour over cooled shortbread crust. Refrigerate until caramel is set, about 30 min.
- FOR CHOCOLATE: Microwave chocolate in a small bowl on medium, stirring halfway through, until almost melted, 2 to 3 min. Stir until completely melted. Pour over caramel layer. Chill until firm, about 1 hour. Remove Millionaires from pans to a cutting board, then cut each into 16 bars.
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