Chocolate Cake:

• Pre-heat your oven to 350F (conventional) and prepare a 9x9" square cake pan with parchment paper and butter / oil
• If making your own buttermilk, mix 2/3 cup milk with 2 tsp vinegar or lemon juice, stir, and set aside
• Mix the flour, sugar, baking powder, baking soda, and salt in a bowl. Sift the ingredients to make sure there are no lumps
• Break in the egg, and add the vegetable oil and buttermilk. Use a whisk to gently mix until the ingredients come together
• In a smaller bowl, mix boiling water with cocoa powder and instant coffee, and whisk until you get a shiny mix. This step blooms the cocoa powder and brings out its lovely chocolatey notes
• Add the bloomed cocoa powder mix to the cake batter, and gently fold until just combined
• Pour the batter into the prepared pan
• Bake at 350F for about ~23-25 minutes until a toothpick inserted into the center comes out with moist crumbs attached
• Let the cake cool down for at least 20 minutes in the pan

Mascarpone Whipped Cream:

• Whisk the chilled heavy cream, sugar and vanilla in a bowl until the cream just becomes thick (do not overmix)
• Add the mascarpone cheese in 2 additions and mix on low speed until combined. Adjust the amount of mascarpone cheese or cream based on your preference of taste and thickness. Do not overmix, the mixture should be thick and fluffy. Overmixing will cause it to become grainy

Assembly:

• Once the cake has cooled down, carefully remove it from the pan and trim off the crust (don't waste too much cake). You can eat the removed part
• Clean the pan and place 2 sheets of parchment paper inside with their ends rising on the edges. Carefully transfer the cake back into the pan, leaving the exposed crumb side on top
• Use a pastry brush to brush on the strong coffee / espresso. You want to go over each part of the cake once, but brush generously, to avoid oversoaking.
• Spread on the mascarpone whipped cream, using an offset spatula to spread it as evenly as possible
• Transfer to the fridge and chill for ~6 hours, or ideally overnight
• Once the cake has set, carefully remove it from the pan, using the edges or parchment paper to lift it up. Transfer immediately to your serving board
• If you want, you can trim off the edges for a neat look
• Use a sifter to dust with cocoa powder
• Slice, serve and enjoy!