Preheat oven to 350F (180C). Line the bottom of an 8-inch (20 cm) square baking pan with parchment paper. Grease the parchment with butter, set aside.
Chop the chocolate and transfer into heat proof bowl, add butter, instant coffee and set the bowl over a double boiler (a pot with simmering water). Melt completely and set aside to cool slightly.
In a large bowl place white sugar, brown sugar and eggs. Beat until light and fluffy.
Add salt, then slowly pour in chocolate mixture while constantly mixing.
Sift int flour and cocoa powder. Fold just until combined. Do not over mix.