Preheat your oven to 350 degrees Fahrenheit. This is the ideal temperature for baking these bars, ensuring that they cook evenly and develop the perfect texture.
Line an 8x8 inch baking pan with parchment paper or tin foil and spray well with non-stick baking spray. This step is crucial for easy removal later on.
In the bowl of a stand mixer fitted with a paddle attachment, beat the cookie butter on medium-high until it’s smooth and creamy. This should take about 2 minutes. You want it to be light and fluffy.
Add in both the light brown sugar and granulated sugar, along with the vanilla. Continue beating for another 2 to 3 minutes, making sure to scrape down the sides of the bowl as needed. This will help incorporate all the ingredients evenly.
Next, beat in the egg and egg yolk, followed by the molasses. Mixing these ingredients well is important for achieving the right consistency.
Turn off the mixer and add in the flour, cinnamon, and salt. Turn the mixer back on at a low speed, mixing just until combined. This should take no longer than a minute. The batter will be very thick at this point, and it's important not to add any more liquid.
Carefully fold in the chocolate chunks, mixing just until combined. At this stage, you want to see those lovely chunks dispersed throughout the batter.
Scrape the batter into the prepared pan and press it down into an even layer. This ensures that your bars will bake evenly.
Bake in the preheated oven for 30 to 32 minutes. The edges should be set and the center may look slightly underbaked, which is perfect for achieving that gooey texture.
Once baked, place the pan of cookie butter bars on a cooling rack. Allow them to cool in the pan for at least 1 hour before slicing. This waiting period is crucial for achieving the right texture.
If you want to add extra chocolate chunks on top, do this right when the cookie bars come out of the oven. Let the chocolate melt slightly before sprinkling them on top.