In a pan over medium heat add in unsalted butter and allow to melt. Once the butter starts bubbling, add white sugar and dark brown sugar.
Mix to combine, remove from heat and add semi sweet chocolate chips.
Stir until the mixture is smooth and set aside to cool.
In a large bowl add vegetable oil, cocoa powder and vanilla extract. Whisk until fully incorporated.
Next, pour in the cooled chocolate/sugar mixture and whisk together.
Then, add in the eggs one at a time making sure to mix completely before adding the next egg.
Fold in flour, salt and baking soda followed by half of the chopped bittersweet chocolate pieces.
Transfer to a greased 9 x 9 baking dish, dollop dulce de leche throughout and swirl into the brownie batter.
Top with remaining chopped bittersweet chocolate pieces and place in a preheated oven at 325F.
Bake for 35-40 minutes until the center of the brownies in the pan are set to the touch (the brownies will keep baking in the hot pan out of the oven). If using the toothpick test, it will not come out with crumbs since this is for fudge-textured brownies.
Allow to cool to room temperature before dividing into pieces. Enjoy!