Step 1

Preheat the oven to 170°C (150°C fan)/325°F/gas 3.

Step 2

To make the biscuit base, put the butter, sugar and both types of flour into a large bowl. Use your fingertips to rub the butter into the other ingredients until the mixture looks really crumbly. Press the mixture into a 23 x 30cm loose-bottomed cake tin (no need to line) and use a palette knife to even out the surface. Bake for 20 minutes, then remove from the oven and cool in the tin on a wire rack.

Step 3

To make the caramel filling, combine the dulce de leche, butter and sugar in a large saucepan over a medium heat. Whisking the mixture, bring to the boil (be careful as the mixture will be extremely hot).

Step 4

Pour evenly over the biscuit base, cover and leave to set for at least four hours or overnight at room temperature.

Step 5

To make the topping, put the chocolate and butter into a medium heavy-based pan and gently heat. Once everything has melted, whisk to combine. Cool slightly, then pour over the caramel and level with a palette knife. Cover, then leave to set overnight at room temperature.

Step 6

Cut into 12 squares to serve.