Preheat the oven to 180C/Gas Mark 4

Grease a 20cm x 20cm baking tin

Sift the flour into a bowl and rub in the butter until it becomes like breadcrumbs.

Add the sugar and mix with your hands until a soft dough has formed.

Roll out to a square and put in baking tin.

Cook in the oven for 10 minutes. Don't allow to brown.

Leave to cool.

Melt the butter and sugar in a saucepan.

Add the condensed milk and bring to the boil, stirring all the time.

Simmer for 5 minutes until thick. Continue to stir to make sure it doesn't stick to the bottom and burn.

Pour the caramel over the cooled shortbread, using the back of a spoon or palette knife to spread it out evenly.

Leave to cool.

Break up the chocolate and put in a bowl over simmering water. Add the butter too.

Stir the chocolate and butter until completely melted.

Pour over the set caramel and spread out to the edges.

Leave to cool for about 1 hour, or until set.

When set, use a sharp knife to cut it into approx 16 squares.