Preheat oven to 350 degrees. Line a 9x13 inch baking dish with parchment paper or aluminum foil, and butter or use nonstick spray. Chop the Oreos and set them aside.
Place caramels in a small saucepan with butter and sweetened condensed milk. On medium-low heat, stir often until caramels are melted and mixture smooth. Set aside.
In a large mixing bowl, cream together the butter and sugar. Add the Biscoff spread (or nut butter) and mix. Add eggs and then vanilla, and mix well.
Combine the dry ingredients: flour, oats, baking powder, and salt in a small mixing bowl. Slowly pour the flour mix into the large mixing bowl. Stir in the chocolate chips and then the Oreo pieces.
Drop about 2/3 of the dough into the prepared casserole pan and smooth it out over the bottom. Slowly pour the caramel mixture over the dough and spread out to the edges. Dollop the rest of the dough on top; don't worry about covering all of the caramel.
Bake for 28-32 minutes. Cool completely and then cut into bars.
OM NOM NOM!