Preheat oven to 350. Line a 8 inch square baking tin with parchment paper. A little cooking spray will help the paper stick to the pan so it doesn't move so much when you pour in the batter.
In a medium bowl mix together flour, cocoa and salt.
In a medium microwave safe glass bowl, add butter, dark chocolate and coffee. Microwave 15 seconds at a time, whisking in between, until butter and chocolate is melted and mixture is smooth and creamy.
Add sugar, vanilla, and eggs and whisk until smooth.
Add chocolate mixture to the flour mixture and using a spatula, gently fold until well combined and gooey. Do not over mix. Pour into prepared pan.
Cook at 350 for 18-20 minutes or until toothpick comes out of center of pan almost clean.
Remove from oven and sprinkle with sel de fleur immediately, if you wish. Cool only slightly. Brownies are best served warm. Perhaps with ice cream.