Before you begin, make sure all your ingredients are measured and ready because once the toffee is cooked, you have to move fast. Place a silicone mat on a large platter or baking tray (non-stick baking paper is ok too, but the mat stays in place). Scatter the peanuts in an even layer on the mat, close together, in a very rough 10x5 rectangle shape.
Now it’s time to make the toffee. In a medium saucepan (sturdy-bottomed with sides at least 3 inches high; I use steel), combine the butter, sugar, salt and vanilla. Place on low heat and stir with a wooden spoon or silicone spatula until the butter has melted.
Once melted, stir constantly (especially if using a thinner saucepan) for another 5 to 8 minutes, until the mixture is a deep golden-brown, like the colour of almond skin. It will go from being foamy and pale to darker within minutes so watch it like a hawk and keep stirring so it doesn’t burn or split.
Immediately pour the hot liquid toffee all over the peanuts and spread evenly to cover the peanuts as quickly as you can because it will start to set almost immediately.
Sprinkle the finely chopped chocolate over the hot toffee and the pieces will quickly begin to melt. Use a metal spatula or spoon to spread the chocolate in an even layer.
Let this cool for a couple of minutes, then drop the melted peanut butter in teaspoons all over the chocolate layer, leaving gaps in between. Use a toothpick or the tip of a knife to swirl it around all over.
Allow to cool at room temperature for about 20 minutes, then place in the fridge for about half an hour until the chocolate has set. Break into pieces with your hands (as big or small as you want) and you’re all done!
Store in the fridge in an airtight tin for 3 to 4 weeks. (The chocolate isn't tempered and therefore will melt at room temperature especially in warmer climates, so I prefer the fridge.)