Add the butter and 2 ounces milk chocolate to a medium size mixing bowl that is microwave safe. Microwave the butter and chocolate on 30 second intervals, stirring after each interval until melted and smooth. To the melted chocolate mixture add the sugar and instant coffee, whisking until completely combined. Then add the vanilla and eggs, whisk until smooth. Next, stir in the cocoa powder, flour and salt until smooth and just combined. Try not to over mix the batter, it will be thick.