1. For the caramel, melt the butter with the brown sugar and Lyle’s Golden Syrup in a large saucepan over a medium heat, swirling the mixture in the pan to prevent sticking.
2. When the sugar has dissolved, allow the mixture to bubble and froth until it turns to a golden caramel colour.
3. Remove from the heat, pour in the double cream and whisk thoroughly until thick and smooth. Sprinkle with the salt.
4. Transfer to a bowl and place in the fridge to cool and thicken.
5. To make the shortbread, beat together the sugar and butter until pale and fluffy. Add the flour, ground almonds and salt and mix together briefly with your hands – do not overwork the dough.
6. Wrap in cling film and chill for about 30 minutes.
7. Preheat the oven to 160°C fan (180°C/350°F/Gas Mark 4). Line 2 baking sheets with greaseproof paper.
8. Roll out the shortbread dough on a lightly floured worktop to about 3mm thick. Cut out heart shapes 5–6cm across the top and place on the lined baking sheet.
9. Re-roll the dough trimmings and continue to cut out heart shapes until the dough is used up. Return to the fridge to firm up for 20 minutes.
10. Bake for 15–18 minutes until lightly golden and set. Keep an eye on the shortbread during baking to ensure that the edges do not catch.
11. Remove from the oven. If the heart shapes have spread a bit, you can trim the edges using the cutter again, but you need to be quick before the biscuits set.
12. Allow to cool for a couple of minutes before transferring to a wire rack to finish cooling.
13. Turn over half of the heart biscuits and dollop a teaspoonful of the thick caramel on to the centre of each base. Set a second heart on top, right way up, and press down lightly. Place the sandwich biscuits in one layer on a flat tray lined with greaseproof paper.
14. Melt the dark chocolate in a heatproof bowl set over a saucepan of simmering water. Drizzle the dark chocolate across each heart sandwich biscuit.