Preheat your oven to 350ºF (177ºC). Grease a 9-inch round cake pan and line the bottom with parchment paper.

In a medium bowl, mix 1 cup of light brown sugar, 1 teaspoon of ground cinnamon, and ½ teaspoon of kosher salt. Reserve some for the streusel.

Add 1 cup of all-purpose flour, ½ cup of cocoa powder, and 2 teaspoons of espresso powder to the remaining sugar mixture. Mix until crumbly and set aside.

In a large bowl, whisk together 1 ½ cups of all-purpose flour, 1 cup of granulated sugar, ½ cup of cocoa powder, 2 teaspoons of espresso powder, 2 teaspoons of baking powder, ½ teaspoon of baking soda, and ½ teaspoon of kosher salt until well combined.

Stir in 1 cup of whole milk, ½ cup of melted unsalted butter, 2 large eggs, and 2 teaspoons of pure vanilla extract until just combined.

Pour half of the batter into the prepared pan. Sprinkle with the reserved streusel, then dollop the remaining batter on top and smooth it out gently.

Place in the oven and bake for 42–45 minutes. Check for doneness by inserting a toothpick; it should come out with a few moist crumbs.

Let the cake cool for 30 minutes in the pan. Then invert it onto a wire rack to cool completely.