Special equipment: an 8-inch square baking pan
Preheat the oven to 350 degrees F. Lightly grease the bottom and sides of an 8-inch square baking pan and line with parchment paper.
Fill a medium saucepan with 2-inches water and set over medium heat. Place the butter and chocolate in a large heatproof bowl, and set over the saucepan, making sure the bottom of the bowl doesn't touch the water. Stir until completely melted. Remove the bowl from the heat and whisk in the cocoa powder until smooth. Add the eggs, one at a time, whisking gently. Whisk in the sugar, cinnamon, vanilla and salt, and then add the flour. Mix in half of the pecans.
Scrape half of the batter into the prepared pan and spread with an offset spatula. Spoon half of the cajeta into the batter and swirl using a skewer or the tip of a knife. Spread the remaining brownie batter on top, followed by the remaining cajeta, and then swirl again to create a marbled effect. Sprinkle the remaining pecans evenly over the top.
Bake on the middle rack of the oven until a toothpick inserted in the center comes out with some crumbs, but the batter isn't wet, 30 to 35 minutes. The cajeta can make it tricky to tell, so check for doneness in a few places.
Cool the brownies, then use a blunt-edge knife to release them from the edge of the pan. Place a piece of parchment over the brownies and top with the back of a sheet pan or a cutting board, and flip out of the pan. Remove the paper from the bottom of the brownies and flip back. Cut the brownies into cubes, and serve.
Cajeta is a goat's milk caramel that you can find at Mexican and Latin groceries as well as specialty food stores.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.