In a small saucepan, melt the butter and leave to cool slightly.
Place the biscuits in the bowl of a food processor.
Blitz the biscuits until they are fine and crumbly.
Add the melted butter and continue processing until the mixture resembles wet sand.
Line the molds of your choice with some of the biscuit mixture, about 1/3-inch high.
Alternatively, place a round biscuit or scone cutter directly onto a tray lined with baking paper.
Press some biscuit mixture into the cutter, about 1/3-inch high, and then carefully remove the cutter to leave behind a nice, round base.
Repeat until all of the biscuit mixture has been used.
Place the lined molds in the fridge for at least an hour for the mixture to firm.
Squeeze the juice of the lemons.
In a large mixing bowl, whisk together the lemon juice, sugar, eggs and cornstarch.
In a medium saucepan, over medium heat, pour in the lemon mixture and cook over medium heat until it thickens.
Pour the lemon curd into a clean bowl, cover with clingfilm in direct contact with the curd, and place in the fridge to cool completely.
Carefully unfold the base of the tarts.
Place a star nozzle into a large piping bag and fill it with the cold lemon curd.
Pipe the lemon curd onto the biscuit bases.
