Step 1: Prepare the Butterscotch Sauce

1. In a medium saucepan, melt the butter over medium heat. Once melted, stir in the brown sugar until dissolved.
2. Slowly pour in the heavy cream, stirring constantly to avoid lumps. Bring the mixture to a gentle simmer and let it cook for 4–5 minutes until thickened.
3. Remove the saucepan from the heat and stir in vanilla extract and sea salt. Let the sauce cool to room temperature.

Step 2: Preheat the Oven and Prepare the Pan

1. Preheat your oven to 350°F (175°C).
2. Grease a 9×13-inch baking pan or line it with parchment paper for easy removal.

Step 3: Make the Brownie Batter

1. In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth.
2. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
3. Sift the flour, cocoa powder, baking powder, and salt into the wet ingredients. Gently fold the dry ingredients into the wet mixture until just combined. Do not overmix.

Step 4: Assemble the Brownies

1. Pour half of the brownie batter into the prepared pan and spread it evenly.
2. Drizzle half of the butterscotch sauce over the batter. Use a knife or toothpick to create swirls.
3. Add the remaining brownie batter on top, spreading it evenly, and repeat the swirls with the rest of the butterscotch sauce.

Step 5: Bake the Brownies

1. Bake the brownies for 28–32 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.
2. Remove the brownies from the oven and sprinkle the top with flaky sea salt while still warm.

Step 6: Cool and Serve

1. Let the brownies cool completely in the pan before cutting into squares.
2. Serve and enjoy the rich, salted butterscotch chocolate goodness!