Make the Cake Batter

1. Dissolve the instant coffee granules into the hot water.
2. In a saucepan, combine butter, chopped chocolate and hot coffee. Heat gently over low heat, stirring constantly until melted. Set aside to cool slightly (must not still be hot). 
3. In a large mixing bowl, whisk together eggs and buttermilk until well combined. Add vegetable oil and mix until fully emulsified.
4. Slowly pour in the cooled chocolate mixture while stirring. 
5. Add vanilla extract and mix combined.
6. Add light brown sugar and caster sugar.   Mix well.
7. Sift in the flour, cocoa powder, baking powder, baking soda, and salt. Use a spatula to help press through any lumps.
8. Gently mix until no dry bits remain using a spatula. The batter may look lumpy at this point so now switch to a whisk and stir until silky smooth.
9. Divide the batter evenly between three 7-inch lined round pans (use scales to achieve even layers). Smooth the tops with an offset spatula.
10. Bake in a preheated oven at 170°C fan for 20–25 minutes or until a skewer comes out clean.
11. Let cakes cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Make the Chocolate Mascarpone Frosting

1. Stir vanilla extract into the double cream and set aside.
2. In a mixing bowl, sift icing sugar, cocoa powder, and salt. Stir to combine.
3. In another mixing bowl, add chilled mascarpone cheese and add in the cocoa mixture.   Gently mix with a spatula to avoid powder flying.
4. Switch to a mixer on medium-low speed to blend until smooth.
5. Add half the cream, mix until incorporated. Add the rest and continue mixing until the frosting is smooth, slightly thick, and spreadable — like soft ice cream.
6. Cover and chill until ready to use.
   

Make the Ganache

1. Finely chop the chocolate (smaller pieces melt more evenly).
2. Pour double cream over the chocolate in a heat-safe bowl. Microwave for 20 seconds.  Stir well.
3. Microwave in 5-second bursts, stirring well after each, until the chocolate is fully melted.  For your reference, mine took 6 bursts.
4. Stir in butter until fully melted for extra shine (optional).

Trim & Level the Cake Layers

1. Use a serrated knife to trim the domed tops off each cake layer for a professional finish (optional).
2. Keep the trimmed domes in an airtight container.  They make a delicious snack. 

Assemble & Decorate

1. Place the first cake layer on an acrylic or cake board.
2. Add a generous layer of chocolate mascarpone frosting. Smooth it out to an even layer.  Repeat with the second layer.  
3. Stack the third layer on top, the flat bottom side facing up to get the perfect level surface. 
4. Apply a thin crumb coat to seal in crumbs. Chill the cake for 60 minutes to set.
5. Frost the entire cake with the remaining mascarpone frosting. Chill for 60 minutes to set. 
6. Spoon the ganache carefully around the edges to create the desired drip effect and then infill the top and smooth finish.
7. Decorate with assorted chocolate bars and chocolate pretzels.