Preheat oven to 180C/350F conventional (see note 1 if using a convection oven with a fan) and grease the bottom and sides of two 8 inch cake tins (mine are 3 inch deep), and also line the bottom of the pans with parchment paper (see note 2).
In a bowl, sift together flour, cocoa powder, baking soda, baking powder and salt. Using a whisk, mix together until well combined. Set aside.
In a large microwave safe bowl, add in butter and dark chocolate. Melt in the microwave for 30 second bursts at a time, mixing in between each burst until fully melted.
Add in cold milk and using a whisk, mix until well combined. This will help cool down your mixture.
Next add in sugar, instant coffee powder, vegetable oil, vanilla and eggs. Using a whisk, mix until well combined.
Add in your pre-sifted dry ingredients and mix with a whisk until combined. Avoid over-mixing.
Lastly, add in your hot water and mix until well combined. Avoid overmixing the batter.
Evenly distribute the batter into the prepared cake tins and bake for 38-40 minutes, or until a toothpick comes out clean. IMPORTANT: Do not open the oven door too early to check the cakes otherwise this can cause the cakes to sink in the middle.
Allow the cakes to cool in the cake tins for 20 minutes, before turning them out onto a wire rack to completely cool (see note 3).