Instructions

• Preheat oven to 350°F. Lightly grease a 9×9-inch baking pan and line it with parchment paper, leaving an overhang on two sides for easy removal.
• In a large bowl, use a hand mixer to cream together 12 tablespoons unsalted butter (3/4 cup), at room temperature, and 3/4 cup light brown sugar (firmly packed) until smooth and combined.
• Add 1 teaspoon vanilla extract and mix briefly to incorporate.
• Add 1-1/4 cups all-purpose flour, 1 cup old-fashioned oats (not steel-cut or quick), 1 teaspoon baking soda, and 1/4 teaspoon salt to the bowl. Mix on low with the hand mixer until a thick dough forms, scraping the bowl with a spatula as needed.
• Divide the dough into two equal portions. Press one portion evenly and firmly into the prepared pan to form the base.
• Measure 1 cup cookie butter (or Biscoff spread) into a microwave-safe bowl. Microwave for 15–30 seconds until warm and pourable; stir and heat an additional 5–10 seconds only if needed. (Take care not to overheat.)
• Bake the prepared base in the preheated oven for 8 minutes. Remove the pan from the oven.
• Immediately sprinkle 1 cup milk chocolate chips evenly over the hot crust.
• Pour the warmed cookie butter over the chocolate chips and use a spatula to gently spread it into an even layer so the chips are mostly covered.
• Crumble the remaining dough evenly over the cookie-butter layer without pressing it down.
• Return the pan to the oven and bake for 13–18 minutes, until the edges are lightly browned and the top is set.
• Remove from the oven and cool in the pan at room temperature for at least 1 hour. Use the parchment overhang to lift the bars from the pan and cut into squares.
• Store the bars in an airtight container; they are best enjoyed within 2–4 days.