Preheat the oven to 160ºc fan and line a 9” square tin with parchment paper
Beat together the butter and sugar until combined
Add plain flour, cornflour and vanilla mix again
Add the chocolate and mix through
Press into the base of the lined tin
Sprinkle over some caster sugar
Bake in the oven for 25-30+ minutes
Leave to cool to let the shortbread set
