Preheat oven to 375° F. Grease eight 4 to 4 ¼-inch tart pans and set them on a baking sheet.
Melt the unsweetened chocolate and butter in a small saucepan over low heat. Set aside to cool slightly.
In the bowl of a standing electric mixer, beat eggs, sugar, corn syrup, vanilla extract, and salt together until light and fluffy, about 10 minutes.
Stir flour and cinnamon into the chocolate-butter mixture, mixing well to combine.
In two additions, gently fold the chocolate batter into the egg mixture. Once it's evenly combined, fold in the chocolate chips.
Using a large ice cream scoop, divide the batter between the prepared tart pans, smoothing the batter as evenly as you can. Don't worry about pushing it all the way to the edges as it will spread out during baking.
Bake until the brownies look just set in the center, about 12 to 15 minutes.
Let cool for at least 10 minutes before removing brownies from the tart pans.
If preparing ahead, reheat before serving, about five minutes in a 300 ° F oven or 10 to 15 seconds each in the microwave.