This recipe was tricky to get just right -- there is a certain pressure when recreating old favourites, but I think I did a good job with this one. The ultimate test is to dip the biscuits into a cup of tea. Makes approximately 25 biscuits.
YOU WILL NEED
For the biscuit dough 250g/9oz unsalted butter, softened, plus extra for greasing
200g/7oz caster sugar
1 large free-range egg, beaten
1 tsp vanilla extract
350g/12oz plain flour, sifted, plus extra for dusting
70g/2Â½oz custard powder
1Â½ tsp baking powder For the buttercream 25g/1oz unsalted butter, softened
140g/5oz icing sugar, sifted
2 tbsps condensed milk
Â½ tsp vanilla extract
For the biscuits, beat together the butter and sugar using a food mixer with a paddle attachment, or with a wooden spoon in a large mixing bowl, until pale and fluffy.
Beat in the egg and vanilla extract, then fold in the dry ingredients with a large metal spoon -- the mixture will come together to form a biscuit dough. Wrap the dough in clingfilm and place in the refrigerator for at least 30 minutes and up to a maximum of 24 hours.
Pre-heat the oven to 200Â°C/fan 180Â°C/Gas Mark 6. You'll need to cook the biscuits in two batches. Roll out half the biscuit dough with a rolling pin on a lightly floured surface until about 5mm/Â¼in thick.
Lightly grease two baking sheets and line with parchment paper. Use a biscuit cutter of your choice -- I used a heart cutter about 5cm/2in in diameter -- to cut out shapes, and place these on the lined baking sheets.
Bake the biscuits in the oven for 10-12 minutes, until lightly golden. Take care not to overcook them, as this will make them brittle -- they are best when still slightly chewy in the centre.
Remove from the oven and immediately transfer to a wire rack to cool. Grease and line the two baking sheets again and repeat the whole process with the second batch of biscuit dough.
Meanwhile, make the buttercream. Beat together the butter and icing sugar in a mixing bowl, then beat in the condensed milk and vanilla extract until smooth.
When your biscuits are completely cool, spread a fairly generous layer (about 2mm/1/16in) of buttercream on to the domed side of one biscuit (so that the biscuit can sit on its flat underside) and top with a second biscuit, flat-side down.
Continue sandwiching together the remaining biscuits with the buttercream.