Prep: Preheat oven to 350°F (175°C). Grease pans and line with parchment paper.
Dry Mix: Whisk flour, baking powder, baking soda, salt, and cinnamon in a medium bowl.
Creaming: In a large bowl, beat butter, oil, and sugars until fluffy (3 mins).
Wet Mix: Add eggs one at a time, beating well. Mix in vanilla and ½ cup Biscoff spread.
Combine: Alternate adding flour mixture and buttermilk to the wet mix. Start with flour, end with flour. Mix just until combined.
Bake: Pour into pans. Bake for 25–30 mins. A toothpick should come out clean.
Cool: Cool in pans for 10 mins, then transfer to a rack to cool completely.
Frosting: Beat butter and ¾ cup spread until smooth. Gradually add powdered sugar and cream. Whip until fluffy.
Finish: Frost the layers and top with crushed cookies.