Step 1: Prepare the Brownie Batter

• Melt the chocolate and butter: In a heatproof bowl set over simmering water, melt the butter, semisweet chocolate chips, and unsweetened chocolate, stirring until smooth. Let cool slightly.
• Combine wet ingredients: In a large mixing bowl, whisk together the eggs, espresso powder, vanilla extract, granulated sugar, and brown sugar until thick and smooth.
• Add the chocolate mixture: Stir the melted chocolate into the wet ingredients until well combined.
• Mix the dry ingredients: Sift together the flour, baking powder, and salt in a separate bowl, then fold them into the wet mixture until just combined.

Step 2: Prepare the Salted Caramel

• Melt the sugar: In a small saucepan, heat the granulated sugar and water over medium heat, swirling the pan (do not stir) until the sugar is melted and turns amber in color.
• Add cream and butter: Remove from heat and carefully whisk in the heavy cream and butter. Stir until smooth, then mix in the flaky sea salt. Let cool slightly.

Step 3: Assemble the Brownies

• Preheat the oven: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan and line it with parchment paper.
• Pour the batter: Spread half of the brownie batter evenly into the prepared pan.
• Add caramel: Drizzle the salted caramel over the batter, leaving some for topping.
• Layer the rest of the batter: Spread the remaining brownie batter on top, gently smoothing it out.

Step 4: Bake the Brownies

• Bake: Place the pan in the preheated oven and bake for 35–40 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
• Cool: Allow the brownies to cool completely in the pan before slicing.

Step 5: Finish and Serve

• Add extra caramel: Drizzle the reserved salted caramel over the brownies and sprinkle with more flaky sea salt, if desired.
• Slice and serve: Cut into squares and enjoy.