• Preheat the oven to 350℉ and line a 8x8 inch baking pan with parchment paper {or spray liberally with nonstick cooking spray}. Set aside.

Biscoff Cookie Crust

• Mix together the crushed Biscoff cookie crumbs with the melted butter until all of the crumbs are coated. Press the mixture into an even layer in the bottom of the prepared pan.

Brownies

• Combine the brownie mix, eggs, water and oil in a large bowl. Mix with a handheld mixer {or by hand} until everything is combined. Pour the brownie batter over the Biscoff crust and spread out into an even layer.
• Add the cookie butter to a microwave safe bowl and microwave for 20 seconds, stir and add 5 second intervals until it is thin enough to swirl. Note: You want the cookie butter to be a thinner consistency but also not too thin. Use a spoon to spoon the cookie butter on top of the brownie batter. Using a butter knife, swirl the cookie butter into the brownie batter, making sure to not disrupt the cookie crust. Finally, sprinkle the milk chocolate chips over the top of the brownie {optional}.
• Bake for 25-28 minutes or until the brownie edges are set and pull away from the pan but the top still has a slight giggle. Remove from the oven, sprinkle with flaky sea salt {if desired} and cool completely before cutting into squares. Store leftovers in an airtight container for up to 4 days. They can also be frozen for up to 3 months.