Melt unsweetened chocolate according to the instructions on the package. Allow chocolate to cool to room temperature.
Brew a small amount strong coffee and place in fridge to cool. (I added some instant coffee to a 1/2 cup of coffee from my Keurig.)
Beat butter and vanilla until light and fluffly.
Add powdered sugar slowly, 1 cup at a time, beating between each cup. (I put my splash guard on my Kitchen Aid mix and left it on low while slowly pouring in the powdered sugar. Then, turned it on high to beat it in, and then repeated the process.)
After the last cup of powdered sugar has been added, scrape down the sides of the bowl and beat for 1 minute.
Add the salt, coffee and heavy cream and beat for 1 minute.
With the mixer on the lowest speed, slowly pour in the room temperature unsweetened chocolate.
Beat for 1 minute on high.
Add more heavy cream, 1 tablespoon at a time, if needed.
Carefully spread over brownies in 9x13" pan.