Preheat oven to 180°C/350°F (fan 160°C)

Grease and line a 28x 18cm (lamington pan) / 7" x 11" rectangle pan with baking/parchment paper (Note 2). Have overhang for ease of removal.

Mix together Base ingredients and press into a pan (I use an egg flip)

Bake for 15 minutes until the surface is golden. Cool in fridge if you have time (Note 3).

Lower oven to oven to 160°C/320°F (fan 140°C)

Place butter, sugar and vanilla in a saucepan over medium low heat. When the butter is melted, whisk to combine with sugar, then just leave it until it comes to a simmer.

When bubbles appear, add condensed milk. Whisk constantly for 5 minutes (Note 4), until you start getting some big slow bubbles on the base.

Once bubbles start appearing, whisk for 1 minute, then pour onto Base. Tilt pan to spread evenly.

Bake for 12 minutes. Don't worry if you get splotchy brown bits (this happens with ovens that don't distribute heat evenly).

Cool on counter for 20 minutes then refrigerate 30 minutes - bottom of pan should be warm but surface cool (not cold) to touch. (Note 5)

Place chocolate and oil in a microwave proof bowl. Microwave in 30 second bursts, stirring in between, until chocolate is fully melted (takes me 4 x 30 sec).

Pour over caramel, spread with spatula. Then gently shake pan to make the surface completely flat.

Refrigerate 1 hour or until set. Remove from fridge and leave out for 5 minutes to take chill out of chocolate slightly. Then cut into bars or squares to serve!