Preheat oven to 350℉. Spray a 9X9-inch square pan with baking nonstick spray. Line the bottom and 2 sides of the pan with parchment paper. Spray again.
In a medium bowl, mix the flour, cocoa powder, cornstarch, and salt. Set aside.
1 cup All-purpose flour, 1 cup Unsweetened cocoa powder, 1 TBSP Cornstarch, 1 tsp Salt
Using a mixer with a whisk attachment, beat the sugar, powdered sugar, eggs, and egg yolk on high speed for 2 minutes.
1 1/2 cups White granulated sugar, 1/2 cup Powdered sugar, 3 Large eggs, 1 Egg yolk
Add in the melted butter, oil, and vanilla and mix on low until combined. Add in the dry ingredients and mix until almost all the way combined.
1/2 cup Unsalted butter, 1 tsp Pure vanilla extract, 1/2 cup Oil
Take off the mixer, add in the chocolate chips. Use a rubber spatula to mix until just combined.
1 cup Semi-sweet chocolate chips
Pour half of the brownie batter into the pan. Pour half of the salted caramel in the pan. Spread over the batter evenly. Leave about 1 inch border around the pan. This will prevent the caramel from hardening after baking. Top with the rest of the brownie batter.
Bake for 40-45 minutes. Brownies are done baking when a toothpick inserted comes out with moist crumbs. If it has batter, bake for another 5 minutes.
Let the brownies cool in the pan on a cooling rack completely.
Remove the cooled brownies from the pan on to a cutting board. Use a skewer to poke small holes all over the brownies. Top with the rest of the caramel. Spread over the holes evenly.
Let it sit for 10 minutes for the caramel to seep into the holes and cut into squares.