Heat oven to 350°F. Line an 8-inch square pan with parchment, leaving overhang.
Melt the butter until just liquid, then cool 3 minutes so it’s warm, not hot.
Whisk melted butter with both sugars until glossy. Stir in vanilla and espresso powder.
Whisk in the beaten eggs until the mixture looks thick and smooth.
In a bowl, whisk flour, cocoa, baking powder, salt, cinnamon, cardamom, nutmeg, and cayenne.
Fold dry ingredients into the wet mixture just until no dry streaks remain.
Stir in chocolate chips, then spread the batter evenly in the prepared pan.
Bake 22–26 minutes, until edges are set and the center shows moist crumbs on a toothpick.
Cool 15 minutes in the pan. Lift out, cool fully, and cut into 16 squares.