Preheat the oven to 180ªC, gas mark 5. Place the flour, cocoa, Lurpak and sugar in a food processor and whizz until well blended. Add the syrup and whizz again to make a smooth dough.
Roll the dough out between 2 sheets of baking parchment then, using a 5cm heart-shaped cutter, stamp out 24 shapes. Transfer to a large parchment-lined baking sheet and bake for 10 minutes
Carefully lift 12 of the biscuits onto a wire rack and reserve. Place a marshmallow half onto each of the remaining biscuits and return to the oven for 1–2 minutes until melted. Sandwich the reserved biscuits on top of each marshmallow and leave to cool – they may need nudging back into position if they start to slip.
Meanwhile, gently melt the chocolate in a heatproof bowl set over a pan of simmering water. Spread a teaspoonful of melted chocolate on top of each sandwich and sprinkle with the dried strawberries and popping candy. Leave to set completely.
For a truly romantic gift on Valentine’s Day, try piping the melted chocolate onto the biscuits to write a personalised message or spell out your loved one’s name. White chocolate works really well, too.