While the caramel cools, make the brownie batter. Preheat the oven to 325 F / 162 C and line and grease an 8x8-inch square metal pan with parchment paper. If you don't have a square pan that size, you can also use a round 8- or 9-inch metal pan. Set aside.
In a medium bowl, mix together 1 1/2 cups sugar, 3/4 cup flour, 2/3 cup cocoa powder, 1/2 cup powdered sugar, 1/2 cup chocolate chips, and 1/2 tsp salt. Set aside.
In a large bowl, whisk together 2 large eggs, 1/4 cup vegetable oil, 1/4 cup melted butter, 2 Tbsp water, and 1 tsp vanilla.
Pour the dry mix into the wet ingredients and stir until just combined. The mixture will be pretty thick, but that's how it's supposed to be!
Pour the batter into the prepared pan and smooth it into an even layer. Bake at 325 F / 163 C for 40-45 minutes, or until a toothpick comes out with a few moist crumbs.
Set it on a wire rack to cool fully before topping. If you want to accelerate the process, place the pan in the freezer for 30 minutes.
Once the brownies are fully cooled, scoop the room-temperature caramel on top and spread it into an even layer.
Add a sprinkle of flaky sea salt, then use a sharp, warm knife to cut into the chilled brownies. Clean the knife after each cut to get perfect slices. Leftover brownies can be kept at room temperature in an airtight container for 2 days, or in the fridge for up to a week.