Preheat oven to 375F. (190 C)
Melt chocolate and butter in a sauce pan on low. Add vanilla and instant coffee, stir to combine. Allow to cool slightly.
In a small bowl combine flour, baking soda and salt.
Beat eggs and sugar together until smooth. Add chocolate mixture and beat until smooth. Then add flour mixture, beat until smooth.
Transfer into a 11 x 16 x 1 pan, lined with parchment paper. Pour batter into pan, and smooth with a spatula.
Bake 10 mins exactly. Allow to cool for at least 30 mins to 1 hour, but overnight even better! (they will get chewier)
Cut into 3 x 3 squares, sprinkle with powdered sugar (icing sugar)