Line a 8 inch square pan with parchment or foil , keeping enough overhang on the sides so you can pull the brownie slab out later . Preheat oven to 180 C / 350 F.
In a bowl, whisk together the water , sugar, salt and vanilla. The sugar might not all dissolve, but it will be paste-like.
In another bowl, melt the chopped chocolate and butter in the microwave or double boiler.
Stir in the cocoa and coffee.
Whisk in the sugar - water - vanilla mixture .
Stir in the flour until combined.
Pour the thin batter into the prepared pan.
Bake for 35 to 40 minutes until a toothpick inserted has only a few wet crumbs.
Cool completely in the pan , remove and slice with a sharp knife.