Preheat oven to 170ºC (340ºC). Line a 8 inch x 8 inch (20cm x 20cm) square baking pan with parchment paper, set aside.
In a small mixing bowl, sift together flour and cocoa. Whisk through salt an set aside.
Prepare a double boiler with a heat proof mixing bowl over simmering water.
Place butter in the bowl then break the chocolate block up into squares and place into the bowl with the butter. Gently melt over a low-medium heat, stirring occasionally. Remove bowl and set aside to cool mixture down for 10-15 minutes until it’s only slightly warm.
In a large mixing bowl, using either electric hand beaters or a stand mixer with the paddle attached, add room temperature eggs, sugar and vanilla. Beat together for 3 minutes, scraping down the sides as needed. The mixture will turn thick and pale.
Once melted chocolate mixture has cooled and is only slightly warm to the touch, pour it into your beaten eggs.
Gently fold chocolate into eggs for about 3-5 minutes until they’re well blended. Take your time as you don't want to lose too much air in those beaten eggs.
Add dry flour mixture and gently fold through until well combined and no pockets of flour remain, ensuring not to over-mix.
Pour batter into lined pan, spread out evenly with a spatula.
Bake for 35-37 minutes or until a toothpick inserted into the middle comes out with some moist crumbs, not completely clean. Slightly under-baking this brownie will create a fudgy center.
Remove from oven and allow to cool in pan for 15 minutes.
Gently lift up sides of the baking paper to remove brownie from the pan. Transfer to a wire rack to cool completely. Still leaving the baking paper on but peeled down completely from the sides.
Slice brownie into squares.
Serve and enjoy!