For the shortbread

450 grams sifted plain flour
115 grams caster sugar
250 grams softened butter

For the filling and topping

450 gram can of condensed milk
250 grams good quality milk or dark chocolate

Method

1. Preheat the oven to 180 C.
2. Butter a 13 x 9 inch baking tray.
3. Mix the flour and sugar in a bowl.
4. Rub the butter into the flour and sugar mixture to form a dough. (You can do this in a food processor)
5. Gently press the dough into the baking tray making sure it’s even. Prick all over with fork to stop it rising too much while it cooks.
6. Bake in the oven for 30 to 35 minutes or until pale golden brown.
7. Remove from the oven and cool for about half an hour.
8. While it's cooling, bring a pan of water to the boil and gently drop in the UNOPENED can of condensed milk. Make sure the water completely covers the can. Leave this to boil gently for about 3 hours. Keep an eye on the pan keeping the water level well above the can and don’t let it boil dry.
9. Once the shortbread has cooled down, spread the warm contents of the condensed milk can on top. Again, leave to cool for about half an hour.
10. Set up a heatproof bowl on top of a pan of simmering  water. Don’t let the bowl touch the water in the pan. Gently melt the chocolate in the bowl.
11. Spread the melted chocolate on top of the cooled condensed milk in the tray. Spread it around so it’s evenly covered.
12. Leave to cool completely before cutting into squares and removing from the tray.