1 ½cups(255g) good-quality chocolate chips or chopped chocolate (see note)
Fine sea salt for the top, optional
Preheat the oven to 350 degrees F. Lightly grease a 9X13-inch metal baking pan with cooking spray (or line with parchment). I haven't tried making these in a glass pan - if doing so, decrease the oven temp to 325 degrees. Set the pan aside.
For the crust, combine all the crust ingredients in a bowl and mix with a handheld or electric stand mixer until evenly combined and no streaks of flour or butter remain, 1-2 minutes. Press the dough evenly in the bottom of the prepared pan. Bake for 13-15 minutes until lightly golden around the edges. Let cool while making the caramel.
For the dulce de leche layer, in a medium pot, combine the all of the caramel ingredients except the vanilla and heat over medium or medium-low heat, stirring constantly with a rubber spatula. Bring the mixture to a gentle boil, scraping the bottom of the pot continuously, and cook for 10 minutes until it changes to a light golden brown color (don't overcook! if the color is changing quickly, don't cook for the full 10 minutes - I keep my heat moderated pretty low, if your heat is higher, the caramel may cook faster). Moderate the heat, especially if it begins to burn on the bottom. Off the heat, stir in the vanilla and immediately pour the caramel over the shortbread crust and spread evenly.
Refrigerate the bars until the caramel is cooled and set, about 30-45 minutes.
For the chocolate ganache, place the chocolate chips or chopped chocolate in a medium bowl. Heat the cream to just below a simmer and pour over the chocolate. Let sit for 1-2 minutes. Stir or whisk until the chocolate chips melt and become smooth. The mixture will go from looking grainy to smooth and glossy. Spread the ganache over the set caramel layer. Sprinkle with sea salt, if desired. Refrigerate until the chocolate layer is set, about an hour.
Cut into slices or squares. To cut neatly, run a sharp knife or bench knife under hot water, wipe dry and slice (repeating as necessary and wiping the knife clean, if needed). If the bars have been refrigerated for a while, let them sit at room temperature for 15 minutes or so to make cutting easier. Refrigerate bars if not serving them within a couple of hours.
Flour: You can experiment using hazelnut flour for part of the all-purpose flour if you like (and if you can find it). You can also try using 100% almond flour (instead of part all-purpose) - when I tried that the crust was more dense and less light and tender, but definitely worth more of a try for a gluten-free option. I have not tried this recipe with 100% all-purpose flour - I think the crust will be quite a bit more dense, but if you want to try it, I'd suggest measuring with a light hand or decreasing the overall flour amount by 1/4 cup. UPDATE: someone suggested using a bit of cornstarch if using all-purpose flour for a tender texture; great idea. I'd suggest replacing 1/4 cup flour with 1/4 cup cornstarch.Chocolate: I use bittersweet or semisweet chocolate chips (Guittard or Ghirardelli). You can experiment with milk chocolate (I haven't tried it myself). As written, this makes a very substantial layer of chocolate (totally my style). You can cut it down, if you'd like the chocolate to be more of an afterthought next to the caramel and shortbread.