Preheat the oven to 150°C/300°F.
Beat the margarine, sugar, vanilla extract, espresso powder, or instant coffee granules, with a K-Beater or hand-mixer for 2-3 minutes, or until it is fully creamed together.
Scrape down the sides of the bowl.
Add the plain flour, semolina, and cornflour to the bowl. Beat for a further 30 seconds to a minute, or until the mixture is just combined.
Scrape down the sides of the bowl again to incorporate any excess. Add the chocolate chips and combine for a further 10-15 seconds.
Lightly grease a 9” x 9” baking pan with margarine.
Carefully spread the fragrant coffee dough into the baking pan to achieve a smooth and level surface.
For that quintessential shortbread look, lightly poke the dough all over with a fork.
Bake in the oven for 35-45 minutes.
To serve, sprinkle caster sugar over the shortbread and cut into squares whilst it’s still hot. Leave to cool for 5-10 minutes, then enjoy!