Step 1: Preheat your oven to 350°F (175°C) and grease a 9×9 inch baking pan or line it with parchment paper for easy removal.
Step 2: Prepare the miso caramel by combining light brown sugar and 2 tablespoons of water in a small saucepan over medium heat. Let it melt and turn into a light amber syrup.
Step 3: Slowly whisk in 1/4 cup of the heavy cream and 2 tablespoons of butter into the sugar syrup. Once smooth, remove from heat and whisk in the white miso paste until fully incorporated. Set aside to cool.
Step 4: In a large mixing bowl, whisk together the melted butter and granulated sugar until well combined.
Step 5: Add the eggs one at a time, whisking vigorously after each addition until the batter is smooth and shiny. Stir in the vanilla extract and melted bittersweet chocolate.
Step 6: Sift in the cocoa powder, flour, and salt. Gently fold the dry ingredients into the wet batter using a spatula until just combined. Do not overmix.
Step 7: Pour the brownie batter into the prepared baking pan, spreading it evenly to the corners.
Step 8: Drizzle the prepared miso caramel over the top of the brownie batter. Use a skewer or a knife to gently swirl the caramel into the batter, creating a marble effect.
Step 9: Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Step 10: Allow the brownies to cool completely in the pan before slicing into 16 squares to ensure the caramel has set properly.