For the brownies: Preheat the oven to 350 degrees F. Line a 9-by-13 inch baking pan with parchment hanging over the edges by about 2 inches (to use as handles for removing the brownies later). Spray the parchment with cooking spray.
Combine the butter and chocolate in a double boiler or bowl set over simmering water and heat, stirring occasionally, until melted.
Combine the granulated sugar, brown sugar, vanilla, salt and eggs in a large bowl. Whisk until smooth. Whisk in the bourbon and melted chocolate. Sift the flour and cocoa powder into the wet ingredients. Stir with a spatula until just combined. Stir in the chopped chocolate thins.
Pour the batter into the prepared pan and smooth with a spatula. Bake on the bottom rack of the oven until the edges are set and a toothpick inserted in the center comes out with a few wet crumbs, 35 to 38 minutes. Cool completely on a rack before frosting.
For the cream cheese frosting: Combine the cream cheese and butter in a mixer fitted with the paddle attachment. Beat on medium-high speed until smooth and light, 1 to 2 minutes. Add the confectioners' sugar and salt and beat on low to incorporate, then increase the speed to medium high and beat until light and fluffy, about 1 minute. Add the bourbon, extract and food coloring. Beat until smooth and pale green in color, scraping down the bowl once, about 30 seconds.
Remove the cooled brownies from the pan and peel off the parchment. Spread the frosting on the brownies in an even layer. Top with the chopped chocolate thins. Cut into squares to serve.