Line an 8x8 inch baking tray with baking paper, and preheat your oven to 180C/350F.
In a bowl, combine Cocoa Powder, Unsweetened Chocolate, Espresso Powder, and Sea Salt. Pour boiling water over and whisk until you achieve a smooth and silky chocolate.
Add Coconut Oil, Sugar, and Vanilla to the mixture and whisk to combine. Leave to cool for 10 minutes. Once cooled, add Flour and Baking Powder to the mixture and whisk till smooth. Fold in Dark Chocolate Chunks and Walnuts.
Pour batter into the lined pan and bake for 22-25 minutes.
Remove the brownies from the oven and let cool completely, before slicing and serving.
TO STORE: Brownies will keep at room temperature in a sealed container for up to 1 week. Store them in the refrigerator if you'd like them to keep longer (but doubt it will last that long!).TO FREEZE: Place brownies in a ziplock bag and store them in the freezer for up to 6 months.