In a mixing bowl, combine flour, sugar, and salt.
In a saucepan, melt butter then add cocoa, stir until well blended.
Add hot coffee/ boiling water and coffee powder, bring to a boil for 30 seconds, then turn off heat.
Pour over flour mixture, and stir.
Combine evaporated milk and egg, baking soda, and vanilla.
Stir well and add mixture into butter/chocolate mixture.
Pour into sheet cake pan and bake at 350-degrees for 15-20 minutes.