Preheat oven to 350 degrees F. Line a 9x9 baking pan or casserole dish with heavy foil allowing foil to hang over the edges. Spray foil including sides with non-stick spray.
In a food processor, combine flour, sugar, and salt. Pulse to combine. Add butter and pulse until it looks like wet sand. Press firmly in the baking dish.
Sprinkle the crust with peanut butter chips, peanuts then Oreos.
In another bowl, whisk Biscoff and sweetened condensed milk until well combined and smooth. Pour over ingredients in baking dish. Spread to cover the entire crust.
Bake 25 to 30 minutes or until edges begins to brown and the center is set. The top will turn from shiny to matte.
Remove from oven and place on a wire rack to cool. Cool completely before cutting. You can refrigerate to speed the cooling time. Bars will cut smoother when cold.
Cut into bars with a serrated knife. Store in refrigeratr in a n air-tight container.