Place the chopped semisweet chocolate and butter in a microwave-safe bowl. Microwave in 20-second intervals, stirring between each, until smooth. Set aside to cool slightly. The mixture should be fluid but not hot.

In a large bowl, beat the granulated sugar and eggs with an electric mixer on medium-high speed for about 2 to 3 minutes, until the mixture is pale, slightly thickened, and falls from the beaters in a slow ribbon.

Beat in the vanilla extract and instant espresso powder. Stir in the melted chocolate mixture until evenly combined and glossy.

In a separate bowl, whisk together the all-purpose flour, cocoa powder, 1/2 teaspoon of the ground cinnamon, baking powder, and salt. Breaking up cocoa lumps now helps prevent dry pockets in the dough.

Add the dry ingredients to the chocolate mixture: Mix on low speed or fold with a rubber spatula just until no visible streaks of flour remain. The dough should be thick, glossy, and sticky rather than firm enough to roll immediately.

Cover the bowl and refrigerate for at least 1 hour. The dough should become firm enough to scoop. If it is still very soft, chill it for another 15 to 20 minutes.

Heat the oven to 350°F (175°C). Line two baking sheets with parchment paper. In a shallow bowl, combine the powdered sugar with the remaining 1/2 teaspoon ground cinnamon.

Scoop the chilled dough into approximately 1-tablespoon portions, rolling each portion gently between your palms. Roll each dough ball generously in the cinnamon powdered sugar mixture until completely coated. A thick coating is important because the dough will expand as it bakes.

Place the coated dough balls about 2 inches (5 cm) apart on the prepared baking sheets. If the dough becomes too soft to handle, return it to the refrigerator for 10 to 15 minutes.

Bake for 10 to 12 minutes, rotating the baking sheet halfway through if your oven browns unevenly. The cookies should be visibly cracked, with edges that look set while the centers remain slightly soft.

Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack. The centers will firm as they cool while remaining soft and fudgy.