Preheat oven to 350°F (175°C) and line a square baking pan with parchment paper.

Melt butter and chopped dark chocolate together in the microwave until smooth. Let cool slightly.

Beat eggs, granulated sugar, and brown sugar on medium-high speed for 3-5 minutes until pale and fluffy.

Fold the melted chocolate mixture and vanilla into the egg mixture until combined.

Sift in the flour, cocoa powder, and salt. Fold gently until no dry streaks remain.

Melt the unwrapped caramels and heavy cream in the microwave until smooth and pourable.

Pour exactly half of the brownie batter into the prepared pan and spread evenly.

Pour the melted caramel over the bottom layer of batter, leaving a small border around the edges.

Dollop the remaining brownie batter over the caramel and spread carefully to cover. Top with crushed pretzels.

Bake for 35-45 minutes. Remove and immediately sprinkle with flaky sea salt.

Cool at room temperature for 2 hours, then chill in the fridge for 1 hour to set before slicing with a hot knife. Drizzle with melted milk chocolate before serving.