Preheat the oven to 325 degrees F.

Grease a 9- by 13-inch baking pan or dish with 2 teaspoons of the butter. Cut a piece of parchment paper 13-inches wide by 17-inches long and press it into the pan so that the bottom and long sides of the pan are covered by the paper. The ends should extend up slightly over the long sides of the pan -- this will form handles which you will later use to remove the brownies from the pan. Grease the paper with 2 teaspoons of the remaining butter.

Heat the remaining butter and the unsweetened chocolate in a saucepan over low heat, stirring constantly, until melted. In a medium bowl, stir together the flour, sugar, cinnamon, and ground chipotle. Add sugar mixture to melted chocolate mixture, stirring to combine. Add eggs, mixing until smooth. Stir in chopped chocolate or chocolate morsels and salt.

Pour mixture into the prepared baking pan or dish. Bake until the center is set, 20 to 25 minutes. Cool on a wire rack until the brownies are firm. Using the two pieces of parchment paper as handles, carefully pull to remove the brownies from the pan and place on a cutting board until completely cooled. Cut into small squares for serving.