Preheat oven to 350 F. Line a 9 x 13-inch baking dish with parchment paper, leaving a 2-inch overhang on the sides for easy removal later. Grease the parchment paper.

In the bowl to a stand mixer fitted with the paddle attachment, mix the butter, sugar, and vanilla extract. Scrape the sides of the bowl.

Add the flour, cornstarch and salt, and mix together until incorporated. Don’t overmix. Shortbread will be sticky. Spread out evenly on the bottom of the prepared baking dish with an offset spatula.

Bake for 21-24 minutes, or until firm and very light golden around the edges.

Let cool for 10-15 minutes. Allow ample time for each layer to cool completely. Rushing this process can cause the layers to mix together improperly. Begin making the brownie batter.

Reduce oven heat to 325°F.

Mix brownie batter together according to package instructions.

Spread evenly over the cooled shortbread crust.

Bake for 28-30 minutes. To ensure the brownies are baked perfectly, insert a toothpick into the center. It should come out with a few moist crumbs, but not wet batter. Brownies will firm up as they cool.

Let cool completely before adding ganache and toppings.

Pour 2 cans of dulce de leche over the cooled brownies. Spread evenly with an offset spatula. Dulce de leche can be thick and sticky. If it’s hard to spread, you can warm it slightly in the microwave to make it more manageable.

Finely chop the chocolate bar and reserve 1-2 tablespoons for sprinkling on top, if desired. Place the remaining chocolate into a bowl.

Pour heavy whipping cream into a small saucepan. Heat over medium heat until hot and just begin to simmer slightly. Pour the hot cream over the chocolate and let sit for 5 minutes. Stir to mix into a creamy chocolate sauce.

Spread ganache over the dulce de leche, and smooth with an offset spatula. Top with pecans. If using the reserved chopped chocolate and coarse salt, place in the refrigerator for about 15 minutes to let the ganache cool slightly. Sprinkle with the chocolate pieces and a little flake salt.

Place in the refrigerator for 2 hours to allow bars to chill prior to cutting. Chilling the assembled dessert for at least 2 hours is crucial. It helps the layers set and makes cutting much easier.

To cut bars, run a sharp knife under hot water, wipe the blade dry, and make one cut through the bars. Wipe the blade and repeat. These will be gooey! These are great served at room temperature or right out of the fridge!