Prepare the Pan: Preheat the oven to 350°F. Grease a 9 × 9-inch square baking pan, then line it with parchment paper. Set the prepared pan aside.
Melt the Chocolate: Place the salted butter and semi-sweet chocolate chips in a microwave-safe bowl. Microwave in 30-second intervals, stirring with a silicone spatula after each interval, until the chocolate has melted completely and the mixture is smooth. Build the Chocolate Base: Transfer the melted chocolate mixture to a large mixing bowl. Add the granulated sugar, vanilla extract, and freshly brewed coffee, if using. Whisk until the sugar has completely dissolved into the chocolate mixture.
Whisk the Eggs: Place the room-temperature eggs in a separate bowl and whisk for 1 minute, or until they become foamy.
Combine the Eggs: Pour the foamy eggs into the chocolate mixture and stir until everything is evenly combined.
Add the Dry Ingredients: Add the all-purpose flour, unsweetened cocoa powder, cayenne powder, smoked paprika, ground cinnamon, and baking powder to the chocolate mixture.
Finish the Batter: Stir the ingredients together just until combined. The finished batter should be thick and slightly runny, with a consistency resembling lava.
Fill the Pan: Pour the brownie batter into the prepared 9 × 9-inch pan and spread it into the pan as needed.
Bake the Brownies: Bake at 350°F for 40–45 minutes, or until the edges are just cooked. The center should still be soft at this stage.
Cool and Set: Remove the brownies from the oven and allow them to cool and set. The soft center will continue to firm as the brownies cool from the residual heat.
Finish with Sea Salt: Once the brownies have cooled and set, sprinkle flaky sea salt over the top, if desired, then serve.