Preheat the oven to 180 C / Gas 4. Slightly grease a 25cm rectangular baking tin.
In a mixing bowl combine the flour, semolina, sugar and butter until well combined and smooth. Press the mixture into the base of the baking tin and prick the surface with a knife to allow the centre to cook evenally.
Bake until firm about 30 to 40 minutes. Leave to cool for around 1 hour.
For the caramel topping, place the butter, condensed milk, syrup and sugar in a saucepan and stir over low heat until the butter melts. Then stir continuously for approximately 10 minutes making sure the mixture does not stick to the base or side of the saucepan. You will notice the colour browning slightly and becoming thicker in consistency. Once it starts to bubble remove from the stove and poor over the shortbread.
Place in the fridge until firm, up to 1 hour, or in the freezer for 30 minutes.
Break the chocolate into small chunks and put in a microwaveable dish in the microwave for 30 second intervals until the chocolate has melted. Evenly pour over the caramel layer and put the tin back in the fridge for up to 2 hours.
When the chocolate surface has completely hardened remove from the fridge. Unmould the shortbread from the tin by tipping it upside down. Cut into squares.