Make the caramel filling first so that it has time to cool before being added between the cookie dough layers. It can also be made up a month in advance and stored in the fridge.

Place a small saucepan over medium heat.

Pour in 1 cup of sugar gradually, adding ¼ cup at a time. Wait until the sugar is mostly dissolved, then add in the next bit of sugar. As the sugar melts it will slowly deepen in color. Stir occasionally until the sugar is fully dissolved and has become a deep amber color, then turn off the heat.

Slowly mix in 6 Tbsp of butter (2 Tbsp at a time), followed by 3 Tbsp of heavy cream and ¼ tsp salt.

Then mix in 1 cup of white chocolate chips. Stir until they're fully melted. The caramel mixture should be pretty thick. Set aside to cool.

Preheat the oven to 350 F / 175 C. Line an 8 x 8-inch or 9 x 9-inch pan with parchment paper and set aside.

Use a stand mixer fit with a paddle attachment or a hand mixer to cream together ¾ cup butter, 1 cup packed brown sugar, and ½ cup granulated sugar in a large bowl. Beat for about a couple minutes, until the mixture is lighter in color and looks fluffy.

Mix in 1 large egg, 1 egg yolk, and 1 tsp of vanilla extract on a medium speed until combined.

Add 2 ¼ cups flour, 2 tsp cornstarch, ¾ tsp baking soda, and 1 tsp salt into the sugar / egg mixture. Mix on low until just combined. Scrape the sides and bottom of the bowl as needed with a rubber spatula.

Mix in 1 ½ cups of your favorite type of chocolate chip on a low speed until they're evenly distributed throughout the dough.

Press ⅔ of the cookie dough (about 730g) into the bottom of the prepared pan. Press it a little bit up the edges of the pan to prevent the caramel from sticking to the side of the pan.

Pour the cooled caramel over the cookie dough. It should be thick, but still fluid enough to spread out with a spoon or offset spatula to create an even layer. If you made the caramel in advance, heat it up in 10 second intervals until you're able to spread it over the cookie dough.

Crumble the remaining cookie dough on top of the caramel with your hands.

Bake for 27-32 minutes, or until the edges are set and golden brown. Rotate the pan halfway through to help them bake evenly.

Place the baking pan on a wire cooling rack and let the bars cool in the pan for a couple hours, or place directly in the freezer and chill for an hour. It's important that you let the bars cool fully before cutting in, or else the caramel will ooze out of them as you cut them!

Use the parchment paper to lift the cookie bars out of the pan, then cut into squares and enjoy. These caramel cookie bars can be stored at room temperature for up to a week in an airtight container.