Heat oven to 350°F. Line an 8-inch square pan with parchment, leaving overhang, and lightly grease.
Melt the butter gently, then let it cool for a few minutes so it doesn’t scramble the batter.
Whisk melted butter with granulated sugar, brown sugar, oil, applesauce, and vanilla until glossy.
In a separate bowl, whisk flour, cocoa, baking powder, and salt. Fold dry ingredients into the wet just until combined.
Stir in chocolate chips. Set aside while you make the caramel.
Microwave caramels with heavy cream in 20–30 second bursts, stirring between each, until smooth and pourable.
Spread about two-thirds of the batter into the pan. Drizzle the warm caramel over. Dollop the remaining batter on top and swirl gently. Sprinkle with flaky salt.
Bake 26–30 minutes, until the edges are set and a tester comes out with moist crumbs. Cool completely, then chill 20 minutes for clean cuts.