To Make the Shortbread Bases
- Roll the shortbread dough into a rectangle 23 × 30 cm/9 × 12 in, 3 mm/⅛ in thick.
- Bake in a 163°C/325°F oven until just beginning to brown, about 15 minutes. Remove from the oven.
- Cut into 6 rectangles 2.5 × 11.5 cm/¾ × 4½ in each. Return to the oven and bake until evenly light browned, about 6 minutes.
- Remove from the oven, set aside, and allow to cool completely.
To Make the Caramel
- Rub the lemon juice into the sugar.
- In a saucepan, caramelize the sugar over direct heat while stirring constantly.
- Add the warm cream slowly while stirring over low heat.
- Remove from the heat and stir in the butter until melted and combined.
- Allow to cool to room temperature.
- Using a disposable pastry bag with a small opening cut in the tip, pipe the cooled caramel into the lined molds, leaving space for the shortbread and the chocolate for sealing the molds.
To Complete the Caramel Shortbread Bars
- Brush the baked and cooled shortbread with melted cocoa butter.
- Place the shortbread bases on top of the caramel in the molds, with the cocoa butter side against the caramel.
- Seal the molds with the tempered dark chocolate. (See Shell-Molding Technique and Theory.) Allow the bars to crystallize at room temperature for 15 minutes.
- Refrigerate the sealed molds for about 20 minutes, until the chocolate pulls away from the inside of the molds.
- Place a piece of stiff cardboard over each mold and invert to release the finished bars.