Grease a 23cm square cake tin with butter.

Sift the flour into a bowl and rub the butter in with your fingertips until the mix resembles fine breadcrumbs.

Add the sugar and mix to form a firm dough.

Press the dough into the base of the prepared tin and prick all over with a fork.

Bake in a preheated oven at 190°C for 20 minutes, until lightly golden. Leave the shortbread to cool in the tin.

To make the topping, place the butter, sugar and condensed milk in a non-stick saucepan and cook over a gentle heat, stirring constantly, until the mix comes to a boil.

Reduce heat and cook for 4-5 minutes, until the caramel is pale golden and thick and is coming away from the sides of the pan.

Pour the caramel over the shortbread base and leave to cool.

When the caramel is firm, melt the chocolate and spread over the caramel layer.

Leave to cool.

Cut into squares or fingers and gently take out.