Preheat the oven to 180°C (or 160°C for fan ovens).

Prepare a 28x 18cm rectangular pan by greasing it and lining it with baking paper, ensuring that there is an overhang on the sides to facilitate easy removal later.

In a mixing bowl, combine all the base ingredients until well incorporated. Transfer this mixture to the prepared pan and press it down uniformly.

Place the pan in the preheated oven and bake for approximately 15 minutes or until the top turns golden. It is advised to cool the base in a refrigerator if time permits.

Adjust the oven temperature to 160°C (or 140°C for fan ovens).

In a saucepan, combine the butter, sugar, and vanilla extract. Place this over medium-low heat. Once the butter has melted, whisk the mixture to ensure sugar integration. Leave the mixture undisturbed until it begins to simmer.

Upon observing bubbles, incorporate the sweetened condensed milk into the saucepan. Continuously whisk this mixture for about 5 minutes, ensuring it doesn’t burn. Once larger bubbles start forming at the bottom, whisk for an additional minute.

Pour the caramel mixture over the pre-baked base, ensuring an even spread.

Place the pan in the oven and bake for 12 minutes. Any browning or splotches on the surface are typical and not a cause for concern. Allow the caramel to cool at room temperature for 20 minutes. Subsequently, place it in the refrigerator for 30 minutes.

In a microwave-safe bowl, combine the chocolate and vegetable oil. Melt the chocolate in the microwave using 30-second intervals, stirring in between each interval until the chocolate is completely melted and smooth.

Pour the melted chocolate over the cooled caramel layer, ensuring a uniform spread.

Refrigerate the Caramel Slice for a minimum of 1 hour, allowing it to set. Once set, remove from the refrigerator and allow it to temper for 5 minutes before cutting it into desired shapes.