SMALL BATCH BROWNIE BASE

1. Preheat the oven to 350°f / 180°c. Grease and line a 9"x5" loaf pan (see FAQ for the exact one I used), leaving the parchment paper extending over the sides to help remove later. If you are worried about it sticking, use two pieces so all edges of the pan are covered with parchment. Secure with binder clips if desired.
2. In a small heatproof bowl over a double boiler (make sure the water does not touch the bowl), or in a heatproof bowl in the microwave, melt together the chocolate and butter. I used the microwave and did it in 15 second increments, stirring after each. Mix until the chocolate is melted and the butter is incorporated. Remove from the heat and add the cocoa, and mix well to combine.
3. In a medium bowl, combine the egg, oil, granulated sugar, brown sugar, and vanilla. Whisk well until thickened and slightly lighter in colour. Add the cooled chocolate mixture and mix until incorporated.
4. Add the flour and salt and mix with a rubber spatula until combined. 
5. Transfer to the prepared pan, and smooth out well. Bang the pan on the counter several times to get it as flat as possible. Bake for 20 to 22 minutes, until the brownie looks set. Remove from the oven and, if desired, using a second loaf pan or the bottom of a drinking glass, gently press the brownie down a little if it has puffed up. Leave to cool completely in the pan. 

BROWN BUTTER PEANUT CARAMEL LAYER

1. Place the butter in a medium saucepan, and place over medium heat. Cook until the butter has melted, and then continue to cook, swirling the pan often, until the butter foams and turns golden brown and nutty - this should take 3-4 minutes. Weigh out 70g (see Notes section below) of the brown butter, and set aside until you are ready to make the caramel.
2. Place the 70g brown butter, sweetened condensed milk, brown sugar, and golden syrup in a heavy bottomed saucepan.
3. Place over a medium heat and stir until melted together, then cook, stirring constantly with a whisk or rubber spatula (I like to use a whisk then switch to the rubber spatula), until the mixture registers 220°f / 105°c on a candy thermometer. Watch the bottom carefully to avoid the mixture catching, turning down the heat if needed or removing the caramel from the heat, stirring well, then returning.
4. Once the caramel has reached the correct temperature, remove from the heat, and add the vanilla and salt. Mix well to incorporate, then add the peanuts and mix to combine. Pour the caramel over the cooled brownie base and smooth off by shaking the pan and using an offset spatula if needed. Transfer to the fridge and allow to set for 1 to 1 1/2 hours or until you can no longer feel heat in it.

CHOCOLATE TOPPING LAYER

1. Melt together the chocolate and the oil in a small heatproof bowl in 15 seconds increments in the microwave, or over a double boiler. Mix until totally smooth. 
2. Remove the pan from the fridge or freezer and pour the chocolate over the top of the caramel filling. Tilt the pan to spread out to cover the filling evenly with the chocolate. Bang the pan a few times on the counter to make sure there are no bubbles. 
3. Place the pan in the fridge and leave to chill for about an hour, or until completely set. 
4. Use the parchment overhang to remove the bars from the pan. Cut into pieces using a sharp knife, wiping between cuts. 
5. Store leftovers in an airtight container in the fridge.