Preheat your oven to 350°F (175°C). Line a 9×13-inch metal baking pan with parchment paper, leaving an overhang on two sides to lift the brownies out later. Lightly grease the parchment with butter or nonstick spray.
nonstick spray or extra butter, parchment paper
In a medium saucepan, melt the butter over low heat. Turn off the heat, add the chopped semi-sweet chocolate, and let sit for 1–2 minutes. Stir until completely melted and smooth.
1 cup unsalted butter, 8 oz semi-sweet chocolate
While the chocolate mixture is still warm, whisk in the granulated sugar and light brown sugar. Whisk for about 1 minute, until the mixture looks glossy and slightly thick.
1 1/2 cups granulated sugar, 1/2 cup light brown sugar
Let the mixture cool for 3–4 minutes so it does not scramble the eggs. Whisk in the eggs and egg yolk one at a time, mixing well after each addition. Stir in the vanilla extract until the batter is shiny and slightly thick.
3 large eggs, 1 large egg yolk, 2 teaspoons pure vanilla extract
In a separate bowl, whisk together the flour, cocoa powder, and fine sea salt. Gently fold this dry mixture into the wet mixture with a spatula just until no streaks of flour remain. Do not overmix.
1 cup all-purpose flour, 1/2 cup unsweetened cocoa powder, 1/2 teaspoon fine sea salt
If your caramel sauce is very thick, warm it gently in the microwave with 2–3 tablespoons of heavy cream in 10–15 second bursts, stirring between each burst, until smooth and pourable but still thick enough to hold ribbons.
1 cup thick caramel sauce or caramel bits, 2-3 tablespoons heavy cream
Pour about two-thirds of the brownie batter into the prepared pan and spread into an even layer. Drizzle or spoon about two-thirds of the caramel over the batter, then sprinkle half of the chopped pecans evenly over the caramel.
1 1/2 cups pecan halves, 1 cup thick caramel sauce or caramel bits
Dollop the remaining brownie batter over the top in large spoonfuls and gently spread to almost cover. Drizzle the remaining caramel over the surface and use a butter knife to make loose, lazy swirls through the batter. Sprinkle the remaining pecans and the mini chocolate chips (if using) evenly over the top, then finish with a light pinch of flaky sea salt.
1 1/2 cups pecan halves, 1 cup thick caramel sauce or caramel bits, 1/2 teaspoon flaky sea salt, 1/4 cup mini chocolate chips
Bake at 350°F (175°C) for 28–35 minutes, or until the edges are set and a toothpick inserted about 2 inches from the edge comes out with a few moist crumbs but no wet batter. The center may still look slightly soft and wobble a bit; it will set as it cools.
Cool the brownies completely in the pan on a wire rack, 1–2 hours. Use the parchment overhang to lift the slab out of the pan. For the cleanest slices, chill the brownies in the refrigerator for 30–45 minutes, then cut with a sharp knife, wiping the blade between cuts.