In a small saucepan, combine Frangelica and 2 tablespoons sugar. Bring to a boil, then simmer until liquid is reduce to about 3 tablespoons of syrup, about 10 minutes.
Preheat oven to 450 degrees. Line a 10-by-15-inch jelly roll pan with parchment paper. Butter and sugar the paper. Separate 9 of the eggs, putting the whites in a mixers bowl and 7 yolks into a medium bowl. (Use remaining yolks for another use.) Add the 2 remaining whole eggs and ¼ a cup of powdered sugar to yolks, whisk until blended.
In the microwave, or in a double boiler, melt chocolate. Put the melted chocolate in a mixing bowl and stir in butter until smooth. Whisk in the egg yolk mixture then stir in cinnamon.
Add remaining powdered sugar to egg white and beat with a mixer until it forms stiff peaks. Fold about 1 cup of the egg whites to the chocolate mixture until blended. Add chocolate mixture to the egg white in bowl and fold in until smooth. Fold in reserved Frangelica syrup, vanilla and half the walnuts.
Pour into prepared baking pan, and use a spatula to spread evenly to the sides of the pan. Sprinkle with remaining walnuts, and fleur de sel evenly over the top. Place in the heated oven. When top is puffed up, about 20-25 minutes, insert knife into the center and see if it comes out clean, if it does then remove from oven. While brownies are still hot, use a paring knife to trim the sides, which may have puffed up over the rim of the baking pan. Place a baking sheet lined with parchment paper on top of the brownies, then invert. Remove top pan and sheet of parchment paper. Let brownies rest at room temperature for 8 hours. Cut into 12 rectangles and enjoy!