Step 1: Preheat Your Oven. Start by preheating your oven to 350°F (175°C). This ensures that your brownies will bake evenly.
Step 2: Prepare the Baking Pan. Grease your 9x13 inch baking pan with butter or line it with parchment paper for easy removal. Set aside.
Step 3: Melt the Chocolate and Butter. In a medium saucepan over low heat, combine 1 1/2 sticks of salted butter and the chocolate chips. Stir continuously until melted and smooth. Remove from heat and let it cool slightly.
Step 4: Mix the Wet Ingredients. In a large mixing bowl, whisk together 1 cup of granulated sugar, 1 tablespoon of instant coffee/espresso, 1 tablespoon of Kahlua, 2 teaspoons of vanilla extract, and 3 large eggs. Mix until well combined.
Step 5: Combine Chocolate with Wet Ingredients. Add the melted chocolate and butter mixture to the wet ingredients. Stir until fully incorporated.
Step 6: Add the Dry Ingredients. In another bowl, sift together 1/3 cup of all-purpose flour, 1/3 cup of unsweetened cocoa powder, 3/4 teaspoon of baking powder, and 1/4 teaspoon of kosher salt. Gradually fold the dry ingredients into the wet mixture using a rubber spatula.
Step 7: Swirl in the Nutella. Gently fold in 1/2 cup of Nutella, creating swirls in the brownie batter. Be careful not to overmix; you want to see ribbons of Nutella throughout.
Step 8: Bake the Brownies. Pour the brownie batter into your prepared baking pan, spreading it evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Step 9: Make the Caramel Sauce. While the brownies are baking, prepare the caramel sauce. In a small saucepan, melt 2 tablespoons of salted butter over medium heat. Add 1/3 cup of granulated sugar and stir constantly until the sugar dissolves. Slowly add 1/4 cup of heavy cream, mixing until smooth. Remove from heat and let it cool slightly.
Step 10: Add Toppings. Once the brownies are out of the oven, drizzle the homemade caramel sauce over the top while they are still warm. Sprinkle with flaky sea salt for a touch of contrast.
Step 11: Cool and Cut. Let the brownies cool in the pan for about 30 minutes. Once cooled, cut them into squares and serve.