Prep an 8x8 or 9x9 square baking pan lined with parchment paper and set aside
Preheat oven to 350°F
In a bowl whisk flour, salt and baking soda and set aside
In a stand mixer with paddle attachment on med-high speed mix together the butter and both sugars for about 5 mins.
Add egg and vanilla and mix for another minute.
Add your flour mixture on low speed and mix until just combined
Finally fold in chocolate chips and Biscoff cookie pieces
Grab your prepared dough and press dough in pan
Spoon cookie butter onto dough and swirl around with a knife
At this time you can top off with extra chocolate chips and Biscoff pieces before baking.
Bake for 20-25 mins, until edges golden brown and just a little soft in middle it will continue to bake and set while cooling.
Let rest in pan for 10-15 mins before transferring it to cooling rack to continue to cool.