Heat oven to 350F. Line a 8 x 12-inch baking tray (I used a 9 x 9-inch) with baking parchment. Put the chocolate, butter and sugar in a pan and gently melt, stirring occasionally with a wooden spoon.

Remove from the heat.

Stir the eggs, one by one, into the melted chocolate mixture. Sift the flour and cocoa, over melted chocolate mixture and stir until combined well.

With a spatula, scrape out the batter into the prepared baking tray. Bake on the middle middle rack for 30 mins or, if you prefer a firmer texture, for 10 minutes more (I baked mine about 45 minutes in a 9 x 9-inch pan).

Cool before slicing into squares.