Heat oven to 180C/160C fan/gas 4.
Line the base and sides of a 20cm
square tin with baking parchment
(the easiest way is to cross 2 x 20cm
strips over the base). Beat the butter,
caster sugar, flour, almonds, baking
powder, eggs, vanilla and the lemon
zest and juice from ½ lemon with an
electric whisk until smooth. Scrape
into the tin and bake for 25-30 mins
until a skewer poked in comes out
clean. Let cool.
Turn out onto a wire rack, trim
edges and slice into 16 squares.
Tip the granulated sugar onto a plate.
Pour remaining lemon juice into
another shallow dish. Very, very
quickly, dip all sides of the cake
squares, one-by-one, into the juice,
then quickly in the sugar. Sit on
a wire rack to set and crisp.