Prepare the cake layers:
Preheat your oven to 180°C (350°F). Grease and line two 8-inch round cake pans.
In a large bowl, whisk together cocoa powder and hot coffee-water mixture. Add vegetable oil, buttermilk, and eggs, and whisk until smooth.
Sift together plain flour, brown sugar, granulated sugar, baking soda, and a pinch of salt in a separate bowl. Gradually add the dry ingredients to the wet mixture, stirring until fully combined.
Stir in the white vinegar and mix well.
Divide the batter evenly between the prepared cake pans.
Bake for 25-30 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.

Make the caramel:
In a medium saucepan over medium heat, melt the granulated sugar, stirring constantly until it turns golden brown. Carefully add the butter, stirring until melted and smooth.
Slowly pour in the warm double cream, continuing to stir until fully combined. Add salt to taste, then remove from heat.
Allow the caramel to cool slightly before using.

Prepare the ganache:
Chop the milk chocolate into small pieces and place it in a heatproof bowl.
In a saucepan, heat the double cream and butter over medium heat until just simmering (do not bring to a boil).
Pour the hot cream mixture over the chocolate and let it sit for 2-3 minutes. Stir until the ganache is smooth and glossy. Let it cool slightly before using.

Assemble the cake:
Place one layer of the cake onto a serving plate. Spread a generous amount of caramel over the top, then sprinkle with chopped peanuts.
Top with the second cake layer.
Pour the ganache over the top of the cake, letting it drip down the sides. Decorate with more peanuts if desired.

Serve:
Let the cake set for 20-30 minutes before slicing and serving.