1. Preheat the oven to 350°F (180°C). Line a 9×13 inches baking pan with baking parchment and set aside. Chop the chocolate and add together with 1/4 cup of the cocoa powder and espresso powder to a large heatproof bowl. Set aside.

2. Add the butter to a saucepan and melt. Let bubble and cook for a moment, then remove from the heat and let sit until there are no more bubbles coming up, then add to the bowl with the chopped chocolate and mix until you get a smooth chocolate sauce. Set aside to cool down a bit.

3. Add the eggs, both of the sugars, vanilla extract, and salt to a large bowl and mix until light and fluffy – for about 8-10 minutes. Add the cooled chocolate sauce and mix in. Mix the flour with the remaining cocoa powder (1/2 cup) and sift into the bowl – gently fold in until just combined. Pour the batter into the prepared baking tin and bake for about 20 minutes. Take out of the oven and drop the pan one or two times on your counter to get some air out – just a bit, you don’t have to smash the half-baked brownies completely :P Sprinkle the brownies with some flaky sea salt (optional) and return the baking tin back to the oven for another 20 minutes or so until the edges are set. Test with a wooden skewer in the center of the brownies – there can be some batter sticking to the skewer, but it should not be liquid. Take out of the oven and let cool down completely on a wire rack. Remove the cooled brownies from the baking tin and cut them into 24 equal-sized bars.