Preheat oven to 325°F. Prepare an 8×8-inch baking pan by lightly greasing it, spraying with nonstick cooking spray, or lining it with parchment paper.
In a medium bowl, combine the brownie mix from the 118-ounce box, ¼ cup water, ⅓ cup vegetable oil, and 1 egg. Stir until well combined and smooth, scraping the bowl as needed.
Spoon about half the batter into the prepared pan and spread it into an even layer with a spatula.
Unwrap the Ghirardelli Dark Chocolate Sea Salt Caramel Squares (16.3-ounce bag). Place the squares directly onto the batter in a single layer, touching slightly but not overlapping; use all the squares from the bag.
Spoon the remaining batter over the chocolate squares in dollops, then gently spread to cover the squares and smooth the top without pressing the squares down.
Bake in the preheated oven for 39–40 minutes, until the edges are set and a toothpick inserted near the center comes out with a few moist crumbs (not raw batter).
Remove the pan from the oven and lightly sprinkle flaky sea salt over the top immediately.
Allow the brownies to cool in the pan for 15–20 minutes before cutting and serving.