Special equipment: two 12-cup nonstick mini muffin tins
Preheat the oven to 350 degrees F.
In a heatproof bowl set over (but not in) a saucepan of gently simmering water, combine the butter, sugar, cocoa powder, cinnamon and salt. Stir continuously until the butter is melted and the mixture is smooth and hot to the touch, about 8 minutes
Remove from the heat and stir with a silicone spatula until cool, about 2 minutes. Stir in the eggs, one at a time, and then the vanilla until the mixture gets very shiny and smooth, about 2 minutes. Your arm may get tired but t10 more stirs and you are done! Now rest for a second, and then fold in the flour. The batter will be very thick.
Spray two 12-cup nonstick mini muffin tins with nonstick cooking spray. Scoop scant 2 tablespoons of batter into each muffin cup, depending on size of tins. Bake until the centers have just set, 6 to 8 minutes. Cool briefly and then invert onto a plate or quarter-sheet tray. While the brownies are upside down, poke 1 piece of broken chip into the bottom. Turn right-side up and serve.